Forget normal SSD drives.
I would get a normal SSD to boot from, and that PCI for storage. Or a raided SSD array for storage.
If he wants things as fast as possible, he won't like the wait for the Raid array to load while booting the system.
Also, no a 360 won't handle all 3 gpus and 990x. You're going to need more rad than that.
I am also on the same boat as don't go 3x580s, simply because there is more room for issue. He is expecting absolutely no hiccups for that price. No need to mess with SLI drivers .