Which 4890 is better?

A $15 price difference is not what I would call "steep" and can be chalked up to the difference between on-line retailers and their supplier agreements as well as the fact that one card is an XFX and the other an MSI.

The XFX has the same cooling heatsink and fan set-up as the Sapphire Vapor-X series of gpu's and I can attest to the quality and effectiveness of that over the Zalmann-ish cooling of the MSI card. Regardless of the fact that the MSI is oc'd 30MHz over the XFX, the XFX card would be the better choice because of the heatsink and fan; plus the fact that you will most likely be able to hit 880MHz or more when/if you oc the XFX.