Best set up for gaming?

Ok, I can either get a 3GB GDDR5 NVIDIA®GeForce® GTX 590 or Dual 2GB GDDR5 AMD Radeon™ HD 6950 or 4GB GDDR5 AMD Radeon™ HD 6990. I have heard that the Hd 6990 is only a mariginal improvment over the Gtx 590, but is $100 dollars more where I am at. I have also heard that the duel Hd 6950 in CF will smoke both of the other cards. But if I get crossfire I won't have enough PCI slots to get a sound card and will have to go with integrated 7.1 channel audio. I can't upgrade my mobo. I also don't know if the Nvidia Phsyx and other things like that are that important to gaming. Should I decide on Nvidia on that and the other perks like 3d gaming already ready to go on their cards unlike Ati? Heat and noise issues are also important to consider. I hear that the GTX 590 is quieter and less hot than the Hd 6990. I don't know if duel HD 6950 heat and noise levels are as bad as the other setups. All in all which setup is the best to future proof my system? Oh the 3gb gtx 590 cost as much as the Crossfire setup. And both of those options are $100 cheaper than the Hd 6990. But if I don't get the Crossfire setup than I can get a dedicated sound card, the Creative Sound Blaster® X-Fi™ Xtreme Audio. Is it worth it? Please use facts, no fanboy comments or flame wars. Sorry for the huge paragraph.