Originally Posted by vuiseng
the bbs just see the battery stats
Aye, but that information allows you to see where your battery is leaking its juice.
2.3 is better for the battery, it's been mentioned on several places before. I never had a 4.1 ROM, but I'm pretty sure an app like Greenify would be unnecessary on a 2.x ROM. Most of those ROMs are very optimized, especially for battery consumption, and minimal user intervention is needed.
Device: Sony Ericsson Xperia X8
ROM: FroyoPro v2.5
Kernel: Stock (11w41)
Clock: 245/729 MHz, Smartass