Re: Not too sure about my new GTX-285 :(
I would imagine you would see a similar increase to what I saw going from an 8800GTS 320 to a Radeon 4770. Performance has increased anywhere from 50-100% in my games. Maybe at your res, the 285 cant really stretch out its legs?
Though with getting lower scores and artifacting there could be a problem with the card itself. I know cpus can downclock if they start getting too hot I'd imagine a video can as well. You didn't remove and reseat the heatsink for some reason did you?