Neoseeker takes a look at two HD 4890's: one from Sapphire, and one from PowerColor, and also, how they run in CrossFire. A quote from the article:

Like NVIDIA's move from 192 shaders to 216 for the first and second version of the GTX 260, and the GTX 285 replacing the GTX 280, ATI is constantly trying to get a leg up on the competition in the fierce, fast and frantic world of video card development. As the sun slowly sets on this generation of cards -- now in April, we are fairly far into the HD 4000's product life-cycle now -- ATI have been applying all that they have recently learnt, into some final designs that will bear the HD 4000 series badge.

>> Sapphire and PowerColor HD 4890 Review