At this point, I don't know that I would invest that much money (looking at $450-$500+ for crossfired 7950s), when the next generation of cards is right around the corner for AMD. It's already here for Nvidia(700-series cards)
If you absolutely have to have an upgrade right now, spend that money on a 770. They're about $400, and they're a good 20-30% more powerful than a lone 7950, and you don't have to mess with crossfire at all. I love crossfire when it works, I had 2 4870s for a couple years, but theres a pretty decent amount of games that either don't work with crossfire at all, of you're waiting for a fix/patch to come out well after release. I always felt a bit screwed when I had 2 cards in my machine and a game would only use 1. Anymore I'd rather just have 1 really nice card.
But regardless of your feeling on crossfire vs single card, I just don't see much point in plunking down $500 on cards that will either be outclassed soon when new ones come out, or at least discounted heavily when new AMD cards hit soon.
Everyone is expecting October/November for AMD 9000-series cards to hit the market.
