I would definitely install this one so the Windows scheduler behaves properly.
http://support.microsoft.com/kb/2645594
There's also another hotfix that disables core parking completely (and increases power consumption), but from what I've gathered in games, apps and general usage it makes absolutely no difference. In fact, I get better performance with core parking on believe it or not. A much better alternative is to use an app to park or un-park on the fly - You might be getting completely opposite results compared to mine. I recommend this one http://bitsum.com/about_cpu_core_parking.php