You kinda got it harry. GTL tweaking is adjusting the "span" between a low and high signal, low being 0, high being one(or the other way around, I dunno).

Anyway, as we increase clocks, the cpu may not be able to match this drop, or it may cause a drop larger than what is set, thereby triggering a "false" 0, fractions of a millisecond early...and thereby destroying stability. So we tweak this to get it jsut right...signal is not read to early, or too late, but this is a function that almost changes as clockspeed increases, not jsut FSB, as the timing left @ high FSB/clockspeeds is less than it would be for a slower speed...so maybe you never get down to .63%, and then never get a 0...

To me, this last line is where cpu's "Wall".