<< Thanks for the answer! But now I'm even more confused. Why would Asus under-clock the chip ? Are the Ti's considered a little unstable at 250mhz ? >>
Not usually, in fact they often tend to be excellent overclockers.
My best guessis that Asus and the other manufacturers marketing Ti VX boards are trying to save a little money buy buying up some of the lesser quality Ti chips that have been fabbed.
As few GTS and Pro cards are manufactured anymore, and the MX boards are based on a cut down GPU, nVidia probably doesnt have much use for the few Ti cores that might not be up to spec to run at 250MHz... so their probably willing to sell them to the card manufacturers relatively cheaply, who can then base Ti VX boards on them, it'd save them a bit of cash and since the GF2 core is mainly memory bandwidth limited it wouldnt be much slower at all either.
Not to mention the average consumer probably doesnt know that the Ti VX is any different then the full Ti, and a few probably purchase the boards under the impression their getting a full Ti.