That's the one I had. I got shadow glitches when I played Modern Warfare 2 in Windows Vista. I hope you have good luck with it. I returned mine.
Just a few minutes ago I got an EFI flash to work on it. I'm getting some screen flickering/ horizontal lines in OS X now, which I'm working on fixing.
If it doesn't work out, I'll just reflash with the original ROM and return it. I think it may just take a little more time to get working smoothly..
EDIT: After re-applying the 10.6.2 Combo update, and then re-doing the QE_CI patch, it now works perfectly as far as I can tell. Framerates are DOUBLE my GTX 285 for Mac in OS X.
So, in summary, this works:
Best Buy's XFX Radeon HD 4890 ZSFR V1.6 "Made in China" (all this info is available on the outside of the box) ~$200.00 USD
Flashed using the attached ROM. I had to do the flash in windows for some reason, but it may have been a glitch with my computer.. your mileage may very in succeeding to flash inside OS X using the ATI Flashing Tool. I also had to re-patch 10.6.2 using the Combo update, but again, your mileage may vary. If you have flickering horizontal lines, the re-patch of 10.6.2 will fix it.
Both the original and the EFI rom are included in my zip attachment.