I've seen that benchmark already, and it doesn't pit the 5770 crossfire with the 4890 crossfire directly, it has the single 4890 and single and double 5770
Use common sense, the 4870x2 is a bit slower than the 5870. So dual 4890's are quite a bit more powerfull than a single 5870 but of course they are not as future-proof. At this point it would be a waste of money if you buy any card/cards other than the 5 series. Dual 5770's are waste of cash IMO cause once you need more firepower you are stuck with both of those cards. On the other hand if you get a 5870 you won't have to worry about upgrading in the future since all you have to do is add another 5850 or 5870. The only cards worth x-firing are 5850's and 5870's IMO... Unless you are the kind that upgrades every 5-6 years.....
My point is that if you have a budget of around 350.00$+ try and get one powerfull card instead of 2 weak cards. This way it will be easier to upgrade in the future without the hassle of selling an outdated GPU/GPU's.