I built a miner and it took a while to get up and running.  Finally I got it going strong at 1100 MHash/sec.  I run it non-stop and have no problems.  It could be pushed further with more tweaking on your end.  Temperatures hover around 55 on 1 5850, 60 on the other, and 65 on the 5870.

Specs:
WD 250GB Sata 6 GB/s 7200 RPM
G.Skill Ripjaws 8GB PC3-10666
AMD Phenom II X4 955 Black Edition
2x XFX HD5850's  - 355 MHash/sec each
Sapphire HD5870 2GB -  400 MHash/sec
Azza Helios 910 Case
MSI 890 FXA-GD70
COOLMAX| ZP-1000B 1000W PSU

I am paypal verified and will only accept payment via paypal, no BTC.  

I have earned quite a few BTC using this rig but its not as profitable as I'd hoped for, and yes I was a noob thinking old money factors would last longer than 10 days.  Looking for $1100 via paypal.

http://www.galleryhosted.com/media/images/thumbs_170/001_DJCKBK9R6JL7YRB.JPG http://www.galleryhosted.com/media/images/thumbs_170/002_DJCKBK9R6JL7YRB.JPG

THE RIG HAS SOLD.