Installed the old reach translator to do some proper comparison testing, and like mist said you pretty much can't tell the difference. I play with a sens of 10 on both and it feels pretty much identical, but because rc1 is closer to 1:1 I get the feeling(imagine) that shots are bit more consistent. That's pretty much my opinion from my first impressions, and after playing while switching back and forth between beta and rc1 I'm sticking with it.
I don't understand how some of you guys are black dotting with 5 sensitivity, 5700 dpi. Maybe I'm just used to the way xim works, but I'm able to play at 10 sens and I rarely have black dot. Try not "flicking" so much, you can do a flick type shot if you just move your mouse slower, but with a higher sens. Maybe your flicking its instantly black dotting and not registering properly or something. Don't know if that made sense, but I'm trying to help, cause it just seems weird.