Before trying this (wich I'm pretty sure won't solve your problem) can I recommend something else?
Download and run this benchmark:
http://www.userbenchmark.com/
It's very simple: download the executable, and when you open it it will run and give you the results. Then compare it to the statistics it will show you and see if your CPU or GPU will be with an info saying it's performing "way below avarage" or something like that. If there's something wrong with your hardware it may alert you and help to find a solution.
It doesn't make sense to be the CPU, cause it works just fine with your GPU (it may cause some bottleneck, but not nearly this much, I say you this cause I have very similar specs).