Can't comment on your Corsair H40 Hydro water cooling because overclocking normally won't help gaming.
Western Digital Caviar Green 1TB HDD runs at 5400rpm ,you'll need a minimum 7200rpm HDD for gaming PC.
Suggest a minimum 650W PSU for a gaming PC.
ATI 1GB Radeon HD 6670 is a low end entry level graphic card, suggest you to get a minimum HD 6850 for your set up.
Forget Crossfire the HD 6670 ,it won't help much for gaming ,get as much a powerful single card as you can afford instead.
iMac Pro review