Crossfire x16 x4 Is there a huge bottleneck?

[Pasatempios]

I have an asus p7p55d mobo which has 2 pci-e 2.0 slots one running at x16 and the other at x4.After looking at this article,I see that the 5870 works at 95% percent with the x4 slot.With the new 6xxx series,I can find many dirt cheap used 5850s and the 5850's price will probably decrease.So do you think it is worth it or should I wait for the 69xx gpus and get that one instead?If you have any experience with such a setup I'd be grateful if you could share it with me.Thanks a lot for any help