The 6200 will blow the 4200 out of the water, even though I probably like my old 4200 better.
I'd actually suggest getting a 6600, as it would be a much better card than a 6200. IMO the 6200 is a lot cheaper of a card versus the rest of its family (6600 / 6800) in comparison to a ti4200 to 4400 / 4600.
Edit: Just looked around a little, and there aren't many choices left. You'd definetely notice an improvement with that card, but I'm not sure what your using it for, because it will lack on most newer titles.