Your board with accept: Socket type: 775
Motherboard supports the following processor upgrades:
Intel Core 2 Quad Q6xx0 with Quad Core technology up to Q6600 (Kentsfield)
Core 2 Duo E6x00 up to E6850 or E6700 (Conroe)
Core 2 Duo E4x00 up to E4400 (Conroe)
The e6850 would be ideal. If you get the q6600, your single core clock speed will drop to 2.4GHz... so for single threaded applications, your current CPU would be faster. So your best bet I think would be the e6850 because it will give you a good clock boost. If you don't play games and are only interested in background activities will multitasking, the q6600 can process double the threads. But the q6600 will kill your games compared to the e6850!