To answer your question, the 480 is not a good choice now that the 580 is available.
2x5870 now costs $500 to $600 after MIR depending on mfg. It is the more expensive, more powerful option.
However, if money is not the issue, I'd buy a 580. I always prefer single vid card solutions where possible. I don't have to deal with crossfire issues, and if by some quirk 1x580 is not enough . . . I can add another later.