Dual mid range cards is still worse than a single high end card, for both amd and nvidia in my opinion. You get more issues with new release games. I have crossfire, and it works fine in the overwhelming majority of my games, but it didn't work in wildstar for the two months I was subbed and it still doesn't work in planetside 2. Planetside 2 in particular is the worst possible outcome for it too, because both cards get loaded and use power but I get the same fps as a single card.
Of course this is all just my opinion, but I wouldn't consider 2 mid range cards instead of one high end card. But crossfire is more than ready for primetime. Particularly the current implementation found on the Hawaii chips.