I had to try locking the phone to 3G only just to test this, and now the phone goes from 100% to 75% in 11 hours. Not much difference from 3G/2G. 2G only is much better for battery life.
If your battery is zapped within 12 hours, you have some ...
If you don't have root explorer, you can log in with adb shell, become root (su -) and type:
mount -o remount,rw /system
Yes, it's basically the same as what you're about to put in hwconfig.sh: it remounts the file system r/w.
I had some problems with battery life the first days using this ROM, even with fairly minimal use. The only irregular thing I could find in Spare Parts' Battery History was Android-system at 50% time under Sensors usage. I haven't checked thorough...