WoW is a VERY OLD game, it is more CPU-bound than GPU when alot of characters are on your screen. In at peak time in loaded server, being in the capical city with 100+ people lowers the FPS of my system (4ghz cpu, oc'ed 7970) to well-below 60. It is normal dont worry.
The most important part is that with a gtx660ti you should still have 60fps in a 10 or 25man raid.
If you are able to buy a simple watercooling solution such as the Corsair H60 or the new Thermaltake Kraken, your CPU will overclocking easily to 4.4Ghz or more. My flatmate has your CPU with the H60 cooler in a mATX case, his temps are never over 60c.