Supply, prices and products can and will change immensely between now and the end of summer, and certainly by Christmas. When you have your cash in hand and are ready to purchase within a week or two, post again to get the best advice at that time.
Any thing proposed now will not be relevant by the time you are thinking to purchase. I would also try to narrow down your price range, as a computer at 800 will be very different than one at 500.
Just my two cents, but I think it will work out better for you in the long run.
BTW, Crossfire and SLI are AMD and Nvidia's technology for using two graphics cards at once to get better performance. Crossfire is AMD, and SLI is Nvidia.