Staying on Mavericks for the long haul - upgrade advice

[InuNacho]

Disclaimer: I'm an artist/prosumer and know the security risks involved in staying on an older OS.

I have a few applications that I use on a regular basis that work best on Mavericks and would like to maximize the usage and longevity of my 2009 Mac Pro. I have the CTO quad 3.33 W3580, 24 GB of ram, and a GTX 680. Using only the internal power supply can I use a 780 even if I plan to occasionally game on Windows using it?
How do the other CPU upgrades whether they be a dual tray I buy off ebay or the single hex stand up my current cpu for something like encoding in Premiere?

Also I have done the firmware hack and it lists my Mac Pro as a Early 2009 and as a 5,1 at the same time. Is that normal?

 

[h9826790]

Also I have done the firmware hack and it lists my Mac Pro as a Early 2009 and as a 5,1 at the same time. Is that normal?

Yes

 

[barmann]

The GTX 780 should work fine --> link .

 

[h9826790]

The GTX 780 should work fine --> link .

Just some extra info. There are 2 versions of 780. Rev A can work natively in Mavericks, Rev B need web driver.