nomorecatering - That is a bit of a beast
I had a tower built for me in December 2010 to my spec, which was aimed at providing my son with a faster platform for rendering 3D animations than the pretty quick Dell M4600 laptop he was using. I already had a NVIDIA Quadro FX 1800, so when I got the new PC I replaced the Zotac (Nvidia) GT220 that it was built with. That was subsequently upgraded to an NVIDIA Quadro K2000
bought on flebay like its predecessor. Anything more powerful than that at the time I got it, was a) way too expensive and b) needed its's own separate power supply and I did not want to get involved in all of that. I'm using a Gigabyte GA-X58-USB3 motherboard and originally I think the PSU was 500w; when it failed I upped this to 650w. The FX 1800 pulled 59w and the K 200 only 51w, both way less than your beast
.
It never did get used for rendering 3D animations, (long story, basically my son had lost interest in becoming an animator after 3 years at uni studying it), but it is great for photo editing
if a bit OTT
What you can put in yours may depend on the size of you PSU more than anything else and I'm guessing that its at least 500w.
Also, replacing the fan(s) may not be too difficult or expensive, they are often just fixed with screws to the graphic card board and power supplied through a plug on fan.
EDITED TO ADD - just looked at my FX 1500, FX 1800 and the GT220 looks like the fans are screwed to heatsinks which in turn are fixed to the board with screws.