Quad core but not impressed.

[Bovidae]

The 8500 may be your culprit. Specs VS the 8800GT:

Core clock: 450Mhz vs 600+MHz
Stream Processors: 16 vs 112
Memory bus: 128bit vs 256bit
Memory clock: 600MHz vs 1800MHz

So you're talking about a card with about 1/3 of the processing power of an 8800GT. If you're talking about running a high-rez single monitor or dual-monitor setup, I can see that being an issue.

This would be my first suspect.

Also, WoW will only run on two cores, #0 and #1 by default. Even then, only sound functions are split to the second core. Take a look at the performance tab of the Windows Task Manager, it may give you some insight to how much you're loading the different cores.

Don't forget to set the processor affinity to #2 and #3 for the second instance, or else you will be slamming your first core, while your other cores are taking a nap. If you turn the sound off, on your slaves, you can asign slaves to run on 1 specific core only: Slave 1-core#1, Slave2-core#2, Slave3-core#3.

If at all possible, do no cross the gap of this dual dual-core chip. Remember, the Q6600 is basicly 2 core2duos on 1 die. There is a bus between cores#0/1 and cores#2/3, but the link between these two chips is considerably weaker.