I was reading yet another nerdfight over the properties and merits of raid configs and was reminded of a site a coworker once showed me: baarf.com. Battle Against Any Raid F.
Ironically, as much as I agree with that sentiment, I recently rolled out a bunch of stuff in mostly raid5 configs because I needed the space, my array has a good sized write cache, and the heaviest write stuff got put on SSD. Also, it was an upgrade from raid1 on 7.2k sata to raid5 on 10k fc, so it was plenty of improvement already.