You dont really want crossfire. Crossfire and SLI are never twice as fast as a single card. Often they only gain around 50% from the second card. What you want is the fastest net GPU power you can fit into your budget.
if you can afford to wait for the 6xxx series in like one or two months they coming out would be an idea time to buy stuff not to mention intel SDD in 25mm are also coming out cheaper and more capacity.