Re: Some advice appreciated
Your resolution has 2.4% more pixels than 1920x1200 so you can go by 1920x1200 benchmarks to see what kind of performance to expect. Generally, a single 480 handles 1920x1200 just fine with the exception of maybe Metro 2033. Also from what I've seen, the difference in performance between 4x AA and 8x is negligible in most games. I would expect a single 480 to be fine, but it all depends on what fps you're used to, so I'd go with one to start with.
I bought both of my 480s at the same time but installed them one by one. When I first booted up BC2 I was quite impressed with single card performance even at 2560x1600, however I was coming from a single 280. I sold both of my 285s a few months before and hadn't played much on them so I couldn't remember well enough to compare.
Also I assume you're running 896MB 260s...if so I wouldn't be too worried about any decrease, the added memory on the 480s will help immensely with AA and large textures.
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