Let's see if you can tell me if this works for you...
One of the things I tell people to try, since I was told the same, is:
When in game, go to Options->Graphics->Details.
There's "Fps cap" value. Lower it. I've it at 25, and the game looks Ok to me.
It's true that I run it windowed, on 800x600 resolution, and that I do nothing risky with it (attack mobs with combo fatalities or read a book inside a library) but so far I experienced a great reduce on cpu usage when playing the game, and no visual loss (that is, you don't see lack of "image refreshing")