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And because both GPUs come standard on video boards with 3.8 ns DDR ram, either card (in theory) has the same memory overclocking potential. A higher core clock does little for performance gain if it does not have the bandwidth to back it up, the GF2 Pro vs the GF2 Ti has proven this... >>
That may be true for GF2 cards, but GF3 cards are more balanced. If you increase the core clock speed it will also improve the effects of the crossbar memory architechture, so it will allow you more memory bandwidth even if the RAM speed is still the same.
I must say that these GF3 Ti500 cards are awesome though.

I'm currently running my Visiontek Xtasy 6964 GF3 Ti500 card at 260/590 (core/mem) from the standard 240/500 speed. Here is my current 3dmark2k1 score of
8246 on a 1.54ghz Tbird.
You should definately pay the extra $35 for the Ti500 over the GF3.