Bigger monitor, which card?

So I run a 19" widescreen (1440x900) monitor now, but am looking to get a cheap (but reliable) 24" in the next few months. It will primarily be for streaming videos (netflix FTW!), but if I can game on it, that'd be great.

I have two questions:

1. In your opinion, is 1920 x 1200 better than 1920 x 1080 for gaming. Is there really any performance difference, I know 1080 has a few less pixels, but does it equate to a real performance impact.

2. What card do you think would be best? I've always stuck with ATI (9800PRO, X800GTO, X850XT, HD 4670), but am open to Nvidia if there's a significant advantage. Right now I'm waiting for the HD 4770 (as some of you have surely figured out), but wouldn't mind grabbing the HD 4850 if the difference is significant.

My Specs:
2.6Ghz X2 Brisbane (OC'd, I might look into getting a Phenom II if my board supports it, or the X2 Kuma and overclocking it, otherwise.)
500watt Antec Basiq
2Gb DDR2 800

I don't have any qualms about turning down video settings in games, and I have little money, so I usually wait 1+ years after they come out to play them, anyway (most recent games I've played are Mass Effect & Stalker: Chernobyl), so if they won't run at Ultra High (or equivalent) settings, that's ok. AA is certainly optional, too (At 1440x900, I very rarely use it). And 30 FPS is perfectly fine in my book, though >25FPS min is more important.

Thanks a lot.

I'm waiting for awhile anyway, both the monitor and GPU upgrades won't be until Fall (so I have my budget set for the next year).

For 1920x1200, a 1GB 4870 would be an excellent card, and they can be had now for under $200. This one is excellent, and comes with a better-than-reference cooler too. Your current card isn't bad though, and if you are only a casual gamer, you might be satisfied with its performance. I'd say try your current card first, and then go for the better one only if you find its performance to be insufficient.

Oh, and go for 1920x1200 IMHO. There's a slight but noticeable difference in the amount of working space (and vertical space is excellent for webpages and productivity), and the performance impact is quite small.