a t2 hyperspatial fit mach does 8.03au/s with the 1-5 HGs and a WS-615 And I think it’s also worth noting you get a nice warp speed bump on frigs/cruisers too if you are doing burners. and it makes doing jita runs much quicker.
Take a look at the warp speed chart from the devblog when they changed things:
System size is a big factor. Bigger systems -> more saved time. Mission spawns are also a factor, if you get mostly in system missions it’s not a big deal, if you have to go 2-3 jumps for every mission it becomes more important. like you say that one system is huge.
Now is it worth it? I couldn’t actually say, haven’t seen a good comparison of with/without. But using the chart lets assume a typical mission is 2 jumps one 50 and one 20au warp, gong from 5au/s->8au/s saves 7s and 5s respectively and you have to go there and back, so that’s 24s in travel time, plus probably another second or two for each gate in mission, and a few more seconds for the warp into the mission. Would estimate the saved time at around 30s per mission.
If you log in and only run a mission or two at a time probably not worth it. If you log in and run for several hours at a time, you can probably get in an extra mission or two per session.
They are great utility implants and there isn’t really anything better to put there. If you got the isk to burn I’d say it’s worth it. But not sure if they are a must have.