Ah, yeah, I see you actually already answered that one before.
Anyway, what do you actually mean with "the sort takes ..."? Displaying the complete folder, including all the thumbnails for the first time (i.e., right after opening the contact sheet), or after you changed the sort order.
Furthermore, how do you measure the time? What is the starting moment, and what determines the action is "ready"?
Is upgrading to PhotoMechanic 4.5.3 the only change you recently made to your system? My guess is that the degradation is caused by something globally, not by PM. Have you tried going back to the previous version does it indeed differ in speed?