There is a sub-forum of the PrPro forae for "Hardware" ... listed in a box to the right side on the initial screen after signing in & choosing the PrPro logo/forum. You might want to check that forum out and post there ...
Sounds like your box should still easily cut through footage at full frame rate w/ CC.
The only thing I would suggest (if your money is burning a hole in your pocket) is to set up a fast RAID... maybe 10,000 rpm or use SSD's.
[Moved to Hardware forum.]
Get the 680GTX card or a moded 770GTX card if those are around.
The storage options would depend on the media. E-Sata will have greater latency than internal drives. If you still have spots for internal drives then I would start there.