upgrade CPU to play Mario Galaxy and DKCR

Hi, first, sorry for my bad english, i hope you can understand me

My Specs:

Asrock Z68 Pro3
i5-2400@stock clock
GTX 570
8 GB RAM

When i play Mario Galaxy (last stable of Dolphin) with LLE (because sound issue with HLE) the framerate drops to 40-50 fps, when the Castle explode in the beginning and the Sound stutters. In Donkey Kong Country Returns also.

I think changing CPU is the best way for me.

http://www.asrock.com/mb/overview.asp?ca...Z68%20Pro3

This is a Link to the supported CPUs for my Motherboard.

Is there a CPU that can solve my problem or do i have to update my Board too?

Thank you and sorry for my bad english