I can confirm a nice, fast drive (I used a 2TB WD Cavier Black 7200 RPM drive as my scratch and media cache drive) yields noticeable improvement over those files residing on the system drive or the project drive.
When I RAIDED my project drive, however, the improvement was not so noticeable. I can say that there was more fluctuation in performance putting all on the one RAIDed drive, though. (ie, Renders showed more consistent high CPU utilization, but utilization tended to dip up and down more).
