I can confirm the Nightmare is great for running L4 missions.
I’ve been using this:
[Nightmare, Spike]
Imperial Navy Heat Sink
Imperial Navy Heat Sink
Imperial Navy Heat Sink
Imperial Navy Heat Sink
Tracking Enhancer II
Damage Control IIAdaptive Invulnerability Field II
EM Ward Field II
Thermal Dissipation Field II
Pith B-Type X-Large Shield Booster
Tracking Computer II
Large Micro Jump Drive
Heavy Capacitor Booster II, Navy Cap Booster 800Tachyon Beam Laser II, Imperial Navy Multifrequency L
Auto Targeting System II
Tachyon Beam Laser II, Imperial Navy Multifrequency L
Tachyon Beam Laser II, Imperial Navy Multifrequency L
Small Tractor Beam II
Tachyon Beam Laser II, Imperial Navy Multifrequency LLarge Capacitor Control Circuit I
Large Energy Discharge Elutriation II
Large Capacitor Control Circuit IHammerhead II x5
Hobgoblin II x5
Since prior to when I stopped playing some time in 2016, and am still using it now without any issues, against all types of mission rats… it may not be optimal but I don’t have to change hardeners for different missions and is able to blitz or full clear depending on what your after. When I first started using it I was using lots of cap charges, these days (more comfortable with ship, better at timing triggers) I can get through most missions with only a few pulses of the shield booster, cap booster is just a safety net.
I would imagine a Phantasm would be able to run L3s, but I haven’t tried it… I like to use the Phantasm for PvP 
PS don’t turn on the auto targeter, it increases the lockable targets without being activated, and is only there to increase lockable targets to 10 (up from 7).
Regards,
Cypr3ss