For current games, a good Ti500 will easily be better than the gf4mx cards. But with the twin vertex shader, they will most probably perform better than the GF3Ti500 for games that use vertex shaders a lot. But then again, games that heavily use vertex shaders won't be out for a while. Look how long it took them to start using T&L, still not 100%.
<font color=red><i>I refugee from Guatanamo Bay,
dance around the border like I'm Cassius Clay
</i></font color=red>