I'm not the expert on this but i just flashed AOKP Milestone 6 a few days ago... LOVING it! You can find the alpha build at xda. So much smoother and faster than stock FF18, and the customization and built in features rock! I've had ok signal using the FF18 modem but the EL29 seems a bit better for my phone. Seems like that issue is different for everyone though, so experiment with modems and see what ya like.
As for battery, I initially had the problems after the stock FF18 update, but fixed them with a combination of cache wiping and a battery pull. I was back to stock GB battery life when I flashed AOKP and my battery is even better on AOKP, and that's using most of its features like the built in weather modules, etc. I honestly think most of the battery issues people are reporting, on any rom, are just battery calibration issues. But that's just me ;-)