Something is definitely not working right. Cause my i5 definitely showed considerable gains over my Q6600 that I had OC'd to 3.2Ghz.
As was mentioned above, a higher powered PSU is not a bad idea to be safe. But biggest concern for me however, is the 2GB of RAM you have. These days, 4GB should really be the target for RAM. With WoW and all the related plugins for it, RAM can actually be somewhat important.
How much RAM did you run on the Q6600/775 setup?
EDIT: Also, with any system update (especially motherboard/chipset changes) it's a good idea to do some driver cleaning and make sure you have the LATEST drivers for all your motherboard chipset stuff. Audio drivers, etc. Then you may want to remove and reinstall the video card drivers as well.