Have you tried to download the latest drivers for your GPU?
I know Kuwese said that if the game worked with the e4500 then dual core isnt a problem, i have a lot of respect for what he says! but i would suggest trying what i said one more time, but this time, running the game, setting the affinty, CLOSE the game, load again. just curious to see what will happen.
I remember going a google search for "games running too fast" when i had the problem and the majority of forums/pages led me to this solution - but again it may be something different.
Did you format and do a clean install or just replace the CPU?