Normally, I would say that you are getting too cute; however, based on what you are showing for your applications, maybe not. I am assuming that you are using this setup either professionally or semi-professionally. Is that true?
If this is true, then I use LOTS of 15K scsi 160 drives professionally for database work and wouldn't use much else. For the RAID you are talking about, much is dependent on the controller you choose. I use a lot of RAID 5, 0+1, and 1. It's expensive, but it is still a far better bang for buck deal (in my opinion) than the Sun servers which we have.
Dave