As far as speed on RAID, it really depends on the hardware. I once did a speed test here at work on an Ultra 2 fibre storage array with Ultra 3 10k drives attached. I was getting around 45 MB per second with Raid 0, 40 with Raid 1, and 37 with Raid 5.

We never recommend Raid 0 though for anything important. Scratch space or temporary things, and it works wonderfully.