First a reminder, these are user to user forums, not a channel to address Adobe directly.
I don't see any slowdown in ACR 8.1 hosted by Photoshop 13.0.5 under Lion 10.7.5 on my MacPro 1,1 Quad.
Try setting the Noise Reduction to zero and tell us if you see any difference.
What exact version of the OS are you running?
Understood. Thanks for this. I have tried using without any noise reduction and have a slight increase in speed to 1-3 seconds before controls become useable. OS 10.6.8
Sorry, logged in with a different email. photoshop user 5674567 is tobylong.
I'm now using a temporary solution. Process in CS5 using the older camera RAW which is very much quicker then, if required, I can convert them to the current RAW in CS6.