I've tried at least 10 different ROM's since I've had my Thunderbolt, and the best I've found so far is Thundershed 1.4 with IMO's 6x kernel. I have the extended battery and I can easily go a full day and have 60-75% battery life left at the end of the day, even when the kernel is overclocked to 1.4!
If anyone is interested, here is a link to the ROM: [CUST][3/09/2012] ThunderShed v1.4 | CM7.2 [android 2.3.7][ICS-ish] - RootzWiki
If anyone is interested, here is a link to the ROM: [CUST][3/09/2012] ThunderShed v1.4 | CM7.2 [android 2.3.7][ICS-ish] - RootzWiki