Currently, Hydra is significantly slower than Crossfire (they couldn't test SLI since the MB didn't support it); sometimes the performance is worse than single card performance. AnandTech encountered bugs and rendering issues even with the "supported" games.
I think right now Hydra is rather pointless. Maybe it would work with a more matured driver and/or a more powerful chip; but if you want more performance ftoday, SLI and CF are much safer bets.
