Re: To GTX 280....or 4870....
Get the 4870 for the res you are playing in.
If you plan on getting a new lcd that supports 1920x1200 in the near future before you upgrade to another card then get a GTX280
The GTX280 is a waste of money at that res. The 4870 can handle that with lots of aa and AF.
And ATI cards will get Physx support also.
Actually ATI brings out more new drivers than nvidia. What you get from nvidia is lots of beta drivers. But you get a lot more updated WHQL drivers from ATI.
And only pure nvidia fanboys will recommend you to buy the GTX280 when you are playing at that res.