I was never able to test out the battery life, as the ROMs I tried had other issues, like no corporate exchange email, etc...
The problem is that it takes a long time to get a really nice ROM. Just grabbing the leak and hacking it and adding a few mods and ripping out some bloat usually breaks some things in the process... and it takes several weeks of people like us installing the ROMs and reporting back all the crap that is broken and doesn't work, for the Devs to start fixing things and make it into what I would consider as a daily driver.
I have tried a gazillion ROM's over the past year on the DX, the TBolt and a couple on the Rezound. Call me biased, but I have yet to use anything as good as CyanogenMod... There are some talented Devs doing cool things to the Rezound, but I have not seen any that I would consider ready for prime time. Camera issues, battery and charging issues, all sorts of little bugs...
To me it isn't worth putting up with that stuff, just to be able to say "I have ICS"... Unless I have the full use of my phone, having ICS is no benefit to me. it's only a benefit if it works. I can use Go Launcher and Go Locker and use ICS themes and have it look like ICS, but actually work properly....