As far as my knowledge goes I believe that to be the case also, there is a weak pull up resistor as part of the CPU but it does very little once you increase vCC above VID and from what I can determine disabling the pull up resistor by maintaining vTT above vCC acts as a limiter / safety against periods of transient overshoot that are more than 10ns or spike above vOS_max which is around 1.1 x vTT iirc.

And yep I've also come to the conclusion that the RF has a couple of voltage bands where vTT works most effectively across the board, 1.34-1.38v for 45 or 65nm and 1.42-1.46v for a heavily oc 45nm or moderate 65nm cpu. I use 1.42v vTT in bios for my q6600 and its the most consistent vTT for my particular setup, 0.63x NB gtlref multiplier for this vTT seems to give a cleaner voltage line when using 1.5-1.6v vNB, and definitely makes using 400mhz strap ( 4:5 divider ) backed with PL of 7 pulled in to 6 on the corresponding phases achieveable at 450+ fsb with a quad core.