I'm running a machine with 3 5850's and have noticed a weird problem. Whenever one of the cards is mining, the other two drop down into the khash/sec range, yet as soon as I stop that one from mining, the other two jump right back up to full speed.
The cards are running on an evga 780i nForce SLI with 2 GB Ram, a Celeron 430 CPU on Win XP. Have Catalyst 10.11 & Stream 2.1 installed. PSU is a Corsair HX850 and even with all of them chugging it rarely goes over 550 watts.
I'm not overclocking at all and not really sure what's going on. Any thoughts?
Update: Updating to 11.5 Catalyst & 2.4 Stream doesn't seem to help. Cards 2/3 are still getting bad speeds and using afterburner I see those 2 GPU's core and memory clocks dipping down from 725/1000 to 157/300 every few seconds.