You could get a 32 inch widscreen to look good as long as it did 1920x1200 hi definition. But going any higher might be pushing it.
Mind you, I can barely output that resolution on a 24" widescreen, and thats not a plasma or anything. But that is with a 7800GT, you'll probably need SLI in the future for the upcomming games, the only real benefit of SLI is the results in hi-res.
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