That is true, to a certain extent.
The first 128MB Ti4200's that came out (AGP2X/4X) were memory clocked at 222MHz (444MHz DDR) compared to the original 64MB ones at 250MHz (500MHz DDR).
Later, they released the Ti4200 with AGP8X which is memory clocked at 256MHz (512MHz DDR).
However, this is all at STOCK speeds. The 64MB Ti4200's, if I'm not mistaken, use 3.6ns memory which would mean they should overclock quite nicely compared to the 128MB Ti4200's that have 4.0ns memory that is 'factory overclocked' by 6MHz (12MHz DDR) out of the box, and likely has less headroom for overclocking.
I know, if you look around hard enough, you can find 128MB ones with better memory, and even special edition ones that are clocked way higher.
<P ID="edit"><FONT SIZE=-1><EM>Edited by spitoon on 11/18/03 10:08 PM.</EM></FONT></P>