the pc im getting has enough room for 2 graphics cards

do i get a single:
1GB ATI Radeon HD 5830 PCI EXPRESS -directX 11

OR

do i get two:
1GB ATI Radeon HD 5750 pci express- directX 11

either way the price will be the same so price doesnt matter

other relative specs:
Screen: 28 inch HD LCD 1080P

Processor: AMD ATHLON II X4 635 (2.9GHZ/2MB CACHE/AM3)
Mother board: ASUS? M4A79XTD EVO: DUAL DDR3, S-ATA II, 2 x PCIe x16, 2 x PCIe x1, 2 x PCI
RAM: 4GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 2GB)
Power; 600W Quiet 80 PLUS Quad Rail PSU 120mm Case Fan
Cooling: SUPER QUIET 22dBA TRIPLE COPPER HEATPIPE CPU COOLER
Hardrive: 250GB SERIAL ATA 3-Gb/s HARD DRIVE WITH 8MB CACHE (7,200rpm)

With all of this in mind which would perform better not only on crysis but most games?

Well, assuming i had the money of course, I would go straight for the1GB ATI Radeon HD 5830 PCI EXPRESS -directX 11, as you say, quality, and very capable, + leaves a PCI express slot available, but thats just my humble opinion

I am just really considering your specs compared to my lower specs also, Athlon ll x4 2.6Ghz, M4A78-EM, 1Gb Ati Rad HD4800 DX10, and so on, i play some top titles with great graphics but not always at very highest settings. I envy you.

from the benchmarks i just googled it looks like the 2 5750 get better results. on the other hand if you buy one 5830 now (good enough for everything right now) you can still at some point upgrade to CF (granted you get a capable mainboard) - which would beat a gtx 295!