(This is not an advert. I like the idea but I dont know if it works well and I dont have anything to do with Pillar other than EnterpriseDB compete against Larry's other little company).
Probably the way to go is flash drives for primary performance data . EMC and others have announced Enterprise Flash Drives (they claim 30 times performance of 15K disks although at 30 times the cost of standard disk today ). Flash should also have pretty much consistent high performance across the whole capacity.
Within a couple of years EFD should be affordable for mainstream use.