I have a "regular" 4x 128MB Ti4200 and I don't understand why everyone wants the 64MB version over the 128 rather than just bumping the memory clock back up to 500MHz for the 128. The 128MB Cards (not the 8X AGP, I am unsure of those) use 4ns RAM chips, which, when you do the math (1000/4ns=250 x 2=500MHz DDR), are rated for 500MHz operation. Nvidia has merely UNDERCLOCKED the 128MB version, so bumping it back up to 500MHz puts it identical to the 64MB version plus the extra 64MB. All you need to do to re-clock the memory back is use the "Coolbits" registry hack which you can easily find on Google. A 64MB card for $99 is NOT a good deal if you plan on playing any upcoming games with reasonable speed, even if it has slightly higher stock memory speed settings.
EDIT: If someone else already explained what I just did, excuse my repeat. I didn't feel like reading through 6 pages of posts to double-check. Also, I have my VisionTek 128MB 4x running at 315MHz Core and 560MHz Memory, which I am sure I could overclock more, but that's the highest that coolbits goes.