I'd suggest setting your CPU affinity for 2 cores each (WoW has some dual-core support). This should allow it to balance the load a little more. You're not going to get any cycles out of your CPU, but it may releave some short term bottlenecks. If you are really bottlenecked at the CPU you can try overclocking a little bit. (Even with stock heatsink and Fan a lot of Q6600 can hit 3.0GHz pretty easy).

Something like this may help a bit
Main - Core 3&4
Clone 1 - Core 1&2
Clone 2 - Core 1&2
Clone 3 - Core 3&2
Clone 4 - Core 4&2
OS and background apps - Core 1