If you use a fixed kernel and turn off all gestures like dt2w and so on your battery life will be fine.
But if you want to use gestures and have good battery life, then you'll also need CM's latest fixes for the proximity sensor.
Both fixes are already included in and tested on Gummy ROM.
The thing with the mpdecision binary is that it keeps two cores active at all time even when it's not necessary.
You can easily avoid this and improve battery life even further if you switch to intelliplug, till the mpdecision binary gets a fix.
Using Gummy, with it's default kernel, I lost 2% in 11h last night while having the phone in deep sleep, with intelliplug and dt2w activated.
So if you're not into CM, or want a liitle more features, Gummy (probably others have these fixes already too, don't know) might be a good choice.
Ps. It also has the latest touch panel drivers included.