Hello,
I have a similar setup at present(your new specs are more powerful... ). I use two workstations for each DAW. Sonar is my preference but many clients feel "more comfortable" with "seeing" pro tools so I have it. I use my Zed R16 ADAT to talk Sonar and PT. I am more comfortable letting my creativeness flow in Sonar and can send that directly to PT via ADAT to a Focusrite Pro 40 PT 11/Digi 002 PT 10 if a client or other party requires it.
My point in mentioning that is this, your hardware pc build wise spects out great. ( I would research to ensure compatibility with the Nvidiia chip set and audio performance). I think a key focus at this point has to be your interface and ensuring that it is also at a level equal to your workstation. High quality Pre's and Converters are to be considered as well as how and what you will be recording. This will relate to the number of inputs/outputs and to the routing flexibillty of the interface. I am not suggesting getting into the technocratic discussions about AD/DA conversion theory and esoteric Pre's vs whatever, I am simply saying there is good information about good equipment out there. Search for it, look at forums like these and if you have any questions, ask.
Having a strong workstation (which you have) and an interface that fits the way you intend to work will on the front end can give you the tools needed to hone your craft and insert some longevity into your setup. With that said, As of November 1st Windows 8.1 is not officially supported by Avid. If stability is a conerstone requirement, It may be prudent to wait for both Avid's approval and more support from 3rd party vendors. X3 (I am almost sure) on the other hand supports Windows 8.1. IHTH