I'm running Harmonia 1.7 right now and getting fantastic battery life (uptime 35 hours @ 50% battery life, using wireless and juice defender. imo.im chat client connecting/updating to three different msging services, made ~90 mins of phone calls, ~1 hour of apps/playing games, ~20 mins of streaming a Netflix episode, ~30-40 mins of web browsing.)
This froyo build (I think the other custom ROMs do as well) also has the fix for the signal drop bug that eats battery life in unrooted, native Optimus V stock --- you can see this happening if you go to Settings -> About Phone -> Battery Use -> click on Cell Standby. If Time Without Signal (or something similar) is present there at >= 50%, you're experiencing the bug.
Since it's rooted I was also able to run SetCPU to overclock the phone. There's several threads here and on XDA about it, but you actually have better battery life and lower temps if you set the minimum clock to 600 rather than the default 240. (Something about it working less hard for commonly used apps/processes).
The only caveat I have about using a custom ROM on this phone is some of the older ROMs (and recoveries) have an issue with some newer Optimus V (mine is a newer one): LG updated the screens to use Optimus S screens (thus needing a different driver than the one used by older ROMs). If you get a blank screen after initial LG logo after flashing a ROM, that's why.
You can overflash with a compatible kernel or use an updated ROM. I had to overflash pica07remix kernel even though Harmonia 1.7 supposedly included an updated version, but it was fine after that.
Just make sure you back up your rom prior to flashing a new rom
EDIT: I have nothing against Gingerbread, I just happen to be satisfied with Harmonia so see no reason to change it, for the now. I do run CM 7.2 Gingerbread (Mirage build) on my Nook Color tablet
