I suspect the difference is my theme, which I didn't have before, xloud, the bravia engine mod, and the newer home launcher version.
The home launcher never showed that much drain on older firmware versions, so I'm guessing the newer one uses more power.
Well guys, I think I found a solution. Some Arc users decided to mix kernels and roms, and discovered a battery fix.
Basically, you install the oldest 2.3.4 version (.283? Something like that anyway) using flashtool, then flash the .42 firmware, but you tell flashtool to exclude the baseband and kernel.
As a result, you have a newer firmware build with an older (better) kernel and baseband.
That way, you end up with battery life how it used to be before the update, BUT you can use themes and mods that are meant for .42, which is the most popular version. I've tested this technique out, and everything is working perfectly.
I already rooted, installed the locked bootloader cwm, flashed a theme, some mods, and a boot animation. Some of those were .42 only, and worked fine, so the kernel must not matter.
I'll have full battery results in a couple of days. The arc users who did it got amazing improvements though.
Also, I enabled gpu ui rendering using the xperia tweak app. Not sure if it's caused by that, or the kernel/firmware combo, but my browsing and general OS use is RIDICULOUSLY smooth right now. I can honestly say I have never seen this phone this fast in the time I've had it since last May.
Sent from Asgard