You will most certainly find using Railguns is the way to go with running level 4’s in a hybrid platform. Most NPC spawns will occur well out of blaster range and with a decent Railgun fit you will whack them without the need to reposition. The range advantage offered by rails over blasters also offers you the ability to fit less tank. Personally I find two normal hardeners, a faction rep, and a pulsing afterburner enough to tank full level 4 rooms. Your damage projection with rails is much better aswell. In a level 4 mission you should be looking at your effective damage around 40 km if you are fast, otherwise 60 km if you are slow.
[Megathron, Megathron PvE - Level 4 Missions - Railgun]
Federation Navy Large Armor Repairer
Armor Thermal Hardener II
Armor Kinetic Hardener II
Adaptive Nano Plating II
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Capacitor Power Relay II
Federation Navy 100MN Afterburner
Large Compact Pb-Acid Cap Battery
Tracking Computer II, Optimal Range Script
Tracking Computer II, Optimal Range Script
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
Large Capacitor Control Circuit I
Large Auxiliary Nano Pump I
Large Nanobot Accelerator I
Hammerhead II x2
Hobgoblin II x1
Ogre II x2
To illustrate my point regarding Railguns vs Blasters, see below;
(Top represents the above fit, using CNAnM, Middle represents above fit but NBC II with Null L, and bottom represents NBC II with CNAnM. I have not included void as your effective damage over time if you are having to hit within 15km in a level 4 means you might aswell run it in a tank bonused battlecruiser)
With that in mind, here are my suggested fits for the megathron hulls in order of ascending value, after the standard issue above.
[Megathron Navy Issue, Megathron Navy Issue PvE - Level 4 Missions - Railgun]
Centus C-Type Large Armor Repairer
Reactive Armor Hardener
Armor Kinetic Hardener II
Armor Thermal Hardener II
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Capacitor Power Relay II
Federation Navy 100MN Afterburner
Heavy Stasis Grappler II
Shadow Serpentis Tracking Computer, Optimal Range Script
Shadow Serpentis Tracking Computer, Optimal Range Script
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
[Empty High slot]
Large Capacitor Control Circuit II
Large Nanobot Accelerator I
Large Nanobot Accelerator I
Hobgoblin II x5
Ogre II x5
Out of all the T1 hulls I think the Navy Issue is the best. For +/- 65m ISK you are sacrificing a little over 100 DPS in the guns compared to a vindicator, but have the ability to fit a heavy grappler (not useful on vindicator) as well as an auxiliary flight of light drones should your heavies not be able to hit anything the grappler has retarded to a stop. Its a utility often overlooked.
[Vindicator, Vindicator PvE - Level 4 Missions - Railgun]
Centus B-Type Large Armor Repairer
Centus C-Type Armor Kinetic Hardener
Centus C-Type Armor Thermal Hardener
Centii C-Type Adaptive Nano Plating
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Magnetic Field Stabilizer II
Core C-Type 100MN Afterburner
Shadow Serpentis Tracking Computer, Optimal Range Script
Shadow Serpentis Tracking Computer, Optimal Range Script
Cap Recharger II
Dark Blood Stasis Webifier
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
Large Capacitor Control Circuit II
Large Auxiliary Nano Pump I
Large Nanobot Accelerator I
Ogre II x5
Slightly faster than the Navy issue, but with an AB its negligable (you’re only using the AB to mess enough with NPC tracking, and to moderately make your way toward any gates while you hit everything with near 100% accuracy on the way). You’re missing a flight of light drones and using a grappler wastes the webifying bonus (although you could use it if you wanted). You do get a bit more DPS.
Now we can consider the big boy Kronos. Even in Bastion I would recommend Railguns. Using the fit Illustrated at the bottom (with NBM II or 425mm RG II) please see the below graphs demonstrating my point.
Kronos - Railguns
(Top is CNAnM, Bottom is Javelin)
To no ones surprise, CNAnM performs better than Javelin, applying 1000 DPS (including hammerhead II) at 60km, vs 50km for javelin, with a better fall off to boot.
Kronos - Blasters
(Top is CNAnM, Bottom is Null)
Showing here that Null is better than CNAnM, by having an extra 10km effective range.
So the assessment with the Kronos is either using blasters loaded with Null, or railguns loaded with CNAnM. I guess then it depends on the missions you are running, but personally I find 1000 dps at 60km superior given most spawns occur at or beyond that range. Remember you are also in bastion, so with blasters you have to wait until the NPC’s get to you, which can take some time.
Anyway, here is a “poorfit” Kronos, to be honest you don’t need to pimp out the tank at all, focus instead on getting good tracking computers and magstabs on there, and also damage implants. Feel free to use an MJD instead of the afterburner, I just prefer afterburners as you don’t have to worry about tank in a marauder, and acceleration gates are never around 100km away.
[Kronos, Kronos PvE - Level 4 Missions - Railgun & Afterburner]
Corpus C-Type Large Armor Repairer
Energized Adaptive Nano Membrane II
Reactive Armor Hardener
Shadow Serpentis Magnetic Field Stabilizer
Shadow Serpentis Magnetic Field Stabilizer
Shadow Serpentis Magnetic Field Stabilizer
Capacitor Power Relay II
Gist C-Type 100MN Afterburner
Heavy Stasis Grappler II
Shadow Serpentis Tracking Computer, Optimal Range Script
Shadow Serpentis Tracking Computer, Optimal Range Script
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
425mm Railgun II, Caldari Navy Antimatter Charge L
Small Tractor Beam II
Salvager II
Salvager II
Bastion Module I
Large Hybrid Collision Accelerator II
Large Auxiliary Nano Pump I
Hammerhead II x5
The standard megathron hull is an extremely viable mission boat, it returns similar numbers to amarr ships which in their relevant space really do shine. You just have to use railguns. To be honest I feel the vindicator is wasted on level 4 missions, you’re better off fitting it for incursions. Use a megathron navy issue instead if you want an expensive t1 hull, but don’t be concerned about using a standard megathron, which definitely have their place as a decent railgun boat (and are probably better suited for missions). Compared to the hyperion, you are simply loosing out on drone DPS. The Hyperions tank bonus does not really contribute much, and that drone DPS is less applicable unless the Hyperion uses sentries (no flight time), in which case weapon DPS needs to be sacrificed for greater tank. Once all factors are considered, the Megathron and Hyperion are comparable and there seems to be no advantage or disadvantage of running one over the other. I would recommend flying the standard megathron hull and aim for a Kronos eventually, don’t waste your money on the navy issue or vindicator (both better suited for PvP and fleet PvE than they are for missions).
and “5th” implants armor\capacitor & navigation or CA series 
