I don't think it is the rate of cooling of different parts that is important, but rather how they are attached - if A and B are connectors that are attached to the frame at X, and connected to each other by touch:
XAAAAAAAAAAABBBBBBBBBBX
When they get cold enough to shrink, they will have less area in contact and eventually no contact:
XAAAAAAAAAA BBBBBBBBBX
Even if the gap is microscopic, it would affect resistance and timing. I _think_ the trick is to build them in a way so that they don't create those gaps, but I'm no HW engineer, and it was a while since I overclocked anything, so take what I say with a spoonful of salt.
John Johnson - Master of Synth.Foods-Convoy|049
Hans Adler - Synth Foods escort wing