You are going top-notch up until you hit a 500GB Barracuda. Even in RAID0... why??? Grab something that will go along with the other power parts you have, like an OCZ RevoDrive (pop it into one of the PCI-E x16 slots). With a read of up to 740MB/s and a write of up to 690MB/s it scorches everything else. Use it for your OS drive and your main programs/games only.
Newegg.com - OCZ RevoDrive X2 OCZSSDPX-1RVDX0100 PCI-E 100GB PCI-Express x4 MLC Internal Solid State Drive (SSD)
For storage, go with the WD Black line. Faster than the Seagates and the WD Blacks have a five year warranty whereas Seagate has dropped theirs to a three year.
The Crosshair IV Formula (should that be the Extreme, or just the regular Formula?) may run 1333 natively, but please don't hamstring the board with it. Go for at least 1600. The Extreme runs 1600 natively, BTW.
With a budget of up to $2K you could build an i7 rig. I will leave that up to those who are more into Intel, though.