As alluded in the original thread, it's likely due to the 200 channels you're on. AFAIK, Vista 32 and 64 have different heap sizes and other internals that could cause slowdowns in one version or another-- you can see an extended discussion of one specific side effect of ~200 channels
here (even less, in that thread). As
Khaled himself says in that thread, there are few things mIRC can do about the resources mIRC uses for channels. Note that that specific issue may not be yours, but it's certainly plausible that they share a common cause given the scenarios.
