I've run every single rom for the Gnex already.. (yes its a problem and I'm seeking help for it ;-) ) and here are All my thoughts:
Stock Pete 4.0.2 - great build. Basicly rooted stock rom and it won't break recovery. I believe its zip aligned too allowing a little better performance.
Revolutionary 2.1.1 - its a solid rom but I found it to be a little glitchy. I don't think its really better then stock and just didn't care too much for it. But that said it is a good alternative. Another thing I noted was that the EXT4 makes it impossible to copy files in the standard mode. Only the camera setting works. FWIW
Fabulous 4.0.2 build - this is my best 4.0.2 choice. Its solid, fast and has a slew of upgrades. It does have the typical slowdowns that all roms have, app drawer stutter, landscape keyboard lag.... but pretty much a well rounded rom.
Mr.Birdman 4.0.3 - best by far. It is AOSP which has its downsides like the lack of the new ringtones, gapps is not as full as a 'rom' would have. Wait for V4 to come out firat though. On V3 the dictionary isn't working and sucks. But the revamps to contacts and alot of the other upgrades in the aosp build make it way faster then any other rom.