I think 850 watts is just a little overkill for that system. I'm using a 550 watt Seasonic with a Q6600 (@3.2GHz), two 640 GB drives in a RAID 0, two optical drives and a GTX 260 (core 216). Plus a few fans and case lights. I would bet 650 watts should be enough.
EDIT: I for to add- I run this at 100% CPU usage 24/7. (I do crunching for World Community Grid)
If you dont plan to crossfire in the future your current board will do fine, and you can save quite a bit by picking up this 620W from seasonic for only $70 before shipping which is better than most 500W units and its a good quality unit http://www.newegg.com/Product/Product.aspx?Item=N82E168...
yea, that's what i thought. hehe. but more pwr aint bad no? the thing is i bought a combo deal for the rams and the psu. hehe. was going for a seasonic x650 but due to price diff. settled for the corsair.