OK, first off, if you are going to run 3dmark, don't use 2003 for your comparison using a Ti4200 since that card will register really low anyway (DX8.1 card compared to the DX9 card of the x800XL). You will want to try 3dmark2001SE which will make your results much closer for the Ti4200 and the x800XL but the X800XL should still give you a higher score. And second, if you want to see what the card will do, try a newer game which came out in the past couple years and not an 4+ years older game for your comparison. Try something like FarCry, HL2 or Doom3 because those we know what the results generally are going to be for that type of hardware. Who knows, maybe those games (F1 Challenge or Nascar 2002) do not work well with newer ATI cards, but I bet it you turned on AA with the TI4200, it would chug too. If your results are still skewed for the cards, then something is having issues, be it drivers, etc.
I realize you sold your card already and you probably can't do these types of tests now (if you've shipped it already), but I bet that x800XL card was a pretty decent card if you were receiving such scores with 3dmark03 (just synthetic, but still). Now if all you want to play are the 4+ year older games, then maybe your Ti4200 is good enough or maybe you can compare to someone's newer Nvidia card such as a GF6600GT if you could borrow one.