Patrick, just so you know, I'm like JJMack and have a workstation like yours (dual Xeon x5690 in my case). Photoshop isn't slow for me - in fact it's the fastest version yet. There may be something specific about your systems that's triggering the behavior.
Do you have a tablet? If so, have you tried removing/updating the tablet driver?
Could you do a Help - System Info like what JJMack did, and post the info here (ideally from both machines on which you've seen the problem)? Maybe someone will be able to spot something amiss (and common) that will reveal new approaches to try.
-Noel