Tempdb drives are much too small. SQL uses tempdb a lot, and you can't afford to run out of tempdb space.
I would not dismiss RAID5 for the db data so quickly. Reads are faster on RAID5, although writes are much slower of course. Proper selection here requires more investigation.
I agree that tempdb data should not be on RAID5, since it is a higher % of write vs read.
SQL DBA,SQL Server MVP(07, 08, 09) "It's a dog-eat-dog world, and I'm wearing Milk-Bone underwear." "Norm", on "Cheers". Also from "Cheers", from "Carla": "You need to know 3 things about Tortelli men: Tortelli men draw women like flies; Tortelli men treat women like flies; Tortelli men's brains are in their flies".