I have a 7850 that refuses to hash at anything above 280 kh/s, not really being stable until 260. It is plugged directly into a x16 slot, and is running alongside two 5850's, one of them on a powered riser. My PSU is 750 watt, but I am using a dual molex to 6 pin pci-e adapter.
System specs:
6 gigs of ram
750 watt Thermaltake PSU
AMD Athlon II X3 2.9 GHz
I'm using GUIminer 0.04 with Catalyst 13.1 and SDK 2.5
Thread concurrency 8124
Worksize: 256
Intensity: 13 (doesn't do any better at higher)
Core: 1120
Mem: 1200
try
Thread concurrency 8192
Worksize: 256
Intensity: 15-19
Core: 1050
Mem: 1200
