Hi,

I'm currently having problems trying to get a computer up with 4x 6870's mining rig going. This is what I have:

Specs:
Asus P8P67 WS Revolution
4x XFX 6870's (16x, 8x, 8x, 8x)
Corsair AX1200 PSU

Drivers/Software/OS:
AMD lastest drivers
ATI APP SDK 2.4
GUIMiner-20110614
Win7 SP1 32-Bit Pro.

I was able to get 3x 6870 to start mining which each of them going at 255+Mhash/s (some higher due to OC'ing. However, once I started the 4th one, all the other GPU's started to drop down between 50-150Mash/s. It would keep on doing that and all GPU's would not max out at 255+Mhash/s.

Anybody have any ideas why this is happening?

I wasn't able to find anything on the forums (based on my searching skills) regarding motherboard only having a max number of GPU's. For what I know, you can have as many GPU's you want on the motherboard no matter how fast the PCI-E lane is whether its 16x 8x 4x or 1x. Correct me if I'm wrong.