Would saphire 5970 4gb crossfire fit on my mobo?

Should fit without issue if your case is big enough as you will need room on the bottom as well... though unless you game on 6 displays it might be a touch overkill  

as daedalus685 said mob isn't going to matter, it still fits in the same out pci-e, but case wise is were it's going to matter as the card is over a foot long

antec 1200

The tricky thing with these is they are thicker than the average 5970.. they are no longer (maybe half an inch).

Since the top card will take up the middle PCIe slot you have to use the 3rd for it, there is a chance it could be very close to the 'floor' of the case; though HIGHLY unlikely in something as massive as an antec 1200.

It will fit... we will be talking like 2grand in graphics cards all told here though...

Thanks for your help. I know it will be very expensive, but this set up would last me a good 4 years