if you're using 5850 xtreme, and you have enough cooling, you should be able to get 400 MH/s, stable. core @ 1020, mem @ 225, 1.2 v.
I'm not using the extreme, my GPU is from one of the first batches when the 5850 released, so it's a full reference model v1 I guess.
I have tried 1.225v max is 990Mhz core