I have a rig I might sell.

It has:

2x Saphire 5850's (PXI-E 16x)
1x XFX 5830 (PCI-E 1x)
Sempron 140

Averages about 950Mh/s with a mild overclock (could easily break 1Gh/s if you overvolt the cards).

Temps are great about 70C tops across all 3 cards.  The 5830 though just sits on top of the case...

As of right now its been running 50 days 24/7.