It also seems that in 2008 adding mirroring also hurt performance. I'm going to dive into this tonight to see if things have changed at all with these benchmarks.

"His results show a single drive maxing out at just under 65MB/s, RAID 0 hitting the ceiling at 110MB/s, RAID 5 maxxing out about 60MB/s, and RAID 10 “F2″ at under 55MB/s."

Summary source: http://www.nevdull.com/2008/08/24/why-raid-10-doesnt-help-on...

Data source (google cache): http://webcache.googleusercontent.com/search?q=cache:Vscz-VX...