First thing I should point out is that you should get a 5770 instead of the 5750. The 5750 is nice, but it's geared to more of an HTPC use. The 5770 has a 15% performance increase over the 5750, which at $15 more, is a massive price to performance gain.
Either of those is plenty powerful for 1280x1024. But you probably can get a 5770 if you get Powercolor's 512mb version(it's cheaper than most 1gb 5750s) since, even with 4xAA enabled, you'll never get close to using 512mb of video memory at that resolution.
Now, if you are planning on upgrading your monitor anytime soon, that's another story.