I believe the 4890 is just going to be a revamped, higehr clocked 4870. It is not new tech from what I have seen, so while it may get closer to the 280GTX, I doubt it will match the 285.
As far as overclocking your card, I suggest just raising one core at a time, the shader seems the most touchy so I would do core, than memory.
I also recommend using Evga Precision for an overclocking utility, its easy to use and you can set different profiles that are easy to change. I have 50% fan while idle then just change profile to go game.
EVGA Precision 1.5.1
For nVidi, its not much different oc'n.
raise core clock about 10MHz at a time and do some testing.
I do ATI Tool artifact scan or OCCT Gpu test for about 15 - 30 min, if no errors are reported I will play agame like crysis or GRID, something that puts a good strain on the card for about 30 - 45 min, if all goes well.
raise n repeat..
I have the OC model from BFG and I run the same shader/mem as the OCX and my core goes a little further. Mine is at 734c for 24/7 gaming, no issues...
I also run 100% fan while gaming, its loud, but temps stay below 70c which I like.
If you fold I would set a seperate profile for that, the shader seems to be the most important as far as that goes so leave others at auto and raise shader as high as possible for folding.Edited by 10acjed - 3/28/09 at 3:16pm