Actually it will give you a very noticable performance improvement in Diablo 3 at the moment.
Currently there is a bug/design oversignt with Diablo 3 where it dosent pre load assets on level load, so when you first start playing every time you use a skill, see a new mob etc it will cause the game to stutter very badly as it's trying to load the assets from the HDD on the fly, unfortunatly most HDD's rnt fast enough to do this at the moment.
I had this issue so copied the game over to my revodrive, bam, instant fix & smooth as silk.