as per your first question, if it has crossfire support this means that it would not offer support for Nvidia SLI. this took me a long time to find. if you go to the ASUS webpage, it will tell you whether or not the motherboard you find on newegg or otherwise supports SLI or Crossfire. so therefore, if you are interested in going NVIDIA and linking 2 cards in SLI later in the future, then getting this MB would not be a good choice. however, if you wanted to do crossfire, this would be the best chocie because it offeres support on board.
SLI may run on it though with certain hacks that you can download, but the rule of thumb is if the motherboard manufacturer says that it doesnt support SLI i wouldnt try it unless you are skilled in that sort of thing
as per the motherboard. i would go to EVGA.com and look at the new line of MB's they just put out. i fully recommend the 680I due to the fact that you would not have to replace it for a long time and it offers x16 to both pci-e slots and the option to get a physix card in the future when they dont suck. it is a little pricey however.
when you go to newegg, be sure to click the MB and then go to the manufacturers website, there are a ton of good one slot x16 mbs out there but they may not offer support for sli, or crossfire. if these things dont matter to you, then the P5B Deluxe is a decent choice.
