I have noticed a faster drain with this beta than the 4.1.2 stable versions, but that's granted. It's a beta!
I have the utmost confidence 4.2 stable release will be amazing, battery & performance & feature wise.
Regardless, I've chosen to follow your tip and replace the marmite kernel included with the ROM and flashed matr1x 24.5 cfs, running on stock clocks with the wheatley governor & ROW scheduler.
I will report back on battery life as well using BetterBatteryStats
I got around 5% drain every 8 hours with the default kernel of Slim Bean 4.2.1 beta1, which was really high, well higher than usual.