It wouldn't make sense for them to put a lot of effort into producing a card that was slower than the 5970, so it will most likely trade blows with it, just so they can claim to be the fastest dual-GPU card available at least part of the time.
Doesn't matter to me either way though. I don't do SLI, even if its on one card... and I cannot imagine the amount of heat and noise this card would generate. I can barely stand my overclocked 470. The fan gets so loud that its actually kind of funny.