Kirk,
No, I don't currently use any code replacements. The contact sheet is already fully loaded, so that can't be it.
I just tried with the IPTC stationary pad: same behaviour (slow with contact sheet, quick with preview).
There must be some interaction between the dialogues and the contact sheet that makes this slow.
On windows I remember that if I placed the cursor at the wrong place, the info tooltip would flicker (I do think this caused slowing down as well, but can't remember 100%). To rule this out, not only did I try to place the cursor outside of the (underlying) contact sheet, I also tried to disable the info tooltip altogether. None of this had any influence...
Can you not reproduce this yourself?
(I do use spaces with 2x2 spaces, but I don't think that has anything to do with it. I have tried killing all other windows, but that too does not influence the behaviour)
Funny things: I tried to see if the processor got used so had the Activity monitor running. I could see no usage spikes, so that's not it. However, when switching a few times between PM with the IPTC window and the activity monitor, sometimes the cursor would move quickly again, and other times not. Even stranger while writing this I have been switching back and forth a lot and sometimes the response is as it should be, and sometimes not. Go figure...
Oh, one more thing, could it be that the keyboard settings (repeat rate and delay) somehow get jammed? The slowness really looks like a "slow" setting in the keyboard preferences. Probably not though as there would be nothing to do so.
Thanks,
Hayo