Try turning your turbo core off for the CPU, and while you are in the bios turn off Hyper-threading too, just to see what happens.
Some say turbo cores fluctuate too much causing dips in play, and maybe the logical cores(hyper threading) are mixing things up too... something to try anyhow.
Also on a side note, the process usage in task manager says "51 processes" in bottom left corner, but only shows about 10 in the window, so hidden processes are running.. maybe other things slowing it down.