True... if you can find a factory pre-overclocked 4850 for RM500++, then I would say go for the 4850. Im using one which is pre-overclocked and comes with 1GB, Im quite satisfied with it.

Anyway, yesterday had a scare with flashing ATI cards in Vista 64bit. Seem like a taboo cos it flash halfway then just stop. Was looking at a RM600 junk and then it went even worse when I killed my bro 3850 the same way. Then this morning, get another Nvidia card and boot again, and rescue both cards. I wont flash over 64bit OS anytime in the future again.

I would say take 4890. You still got an option to add the second card if you happened to need it.

If you aint bothered and just wanna wait for DX11 spec, then start saving your money. It does feel like GPU maker are clearing stock by hefty discount while waiting to launch DX11 part along with Win7. Just my guesstimate.