if you can change out the WD Green drive for a black version because they are faster
The Caviar Black drives are good no question but the premiums on them right now with the HD shortages are ridiculous - they're not worth it right now. When they drop in price they'll be worth it absolutely.
If you fill this out we can better assist you: http://www.tomshardware.com/forum/261222-31-build-advice
In the meantime I'd suggest not using a 5900RPM as your primary HD - it will be a huge bottleneck.