For further infos you should follow the original rage kernel thread.
2.9 is based on 2.8 with optimized governors.
I am currently testing and comparing 2.9 with 2.7.
Today 2.9, tomorrow 2.7.
Well. 2.9 seems fine. As dumohsmol suggests, smartassV2 seems best ogevernor for 2.9 (was running ondemand - my preferred - but in this smartassv2/ondemand comparison it lost). Idle behavior is very good, also with some background data running. But as well as in 2.8 the cpu workload is a bit higher than in 2.7. But all in all it feels smoother. But it seems the low consumption in idle now eats the usage drain
But this is very depending on YOUR usage.
will report later.