It appears that although Adobe has some very deep pockets, that they didn't bother to hire engineers with experience using GPUs in gaming environments. I am no SME on this but a quick search of the forums and the internet show that the ability of the GPU is hampered by the scheme used by LR.
I am sure that things will get better. In fact, for editing I simply skip over to Bridge and use camera raw. It is much faster and doesn't have the jerky behavior LR has on my computer.... "Your mileage my vary"
Wolf, I did read the explanation and found it to be a ton of excuses for poor development decisions. Regardless I have a friend using a much lower end nvidia gaming card. It is *not* experiencing this performance issues image to image. This means it's either specific to the OSX version, ATI/AMD, or some combo.
J.P. Owens, You nailed it, the development is truly a joke at this point. I'm really down right sick of waiting at this point. Lightroom's piss poor implementation of OpenGL redraws with not a breathe of OpenCL makes me wonder what I've been waiting and paying into for a few years now. At the very least a public beta (which I feel I am now part of) to ensure hardware compatibility. Being they couldn't even optimize to common and known configs (Mac Pro, iMac, etc) shows a blatant disregard to their paying customer base.
I'm not one to take to forums and complain like this but it seems like it's only venue at this point. Although I'm sure this falls on deaf ears as well. If Adobe listens it's silent to response in words or action. Capture One among countless apps (photo and video) have zero problems implementing GPU support and general hardware scaling. It appears no matter what you provide LR it will remain stagnant or in this case perform worse! The statement from the lead engineer that stands out is "3. Using the GPU involves some overhead (there's no free lunch). This may make some operations take longer, such as image-to-image switching or zooming to 1:1. Newer GPUs and computer systems minimize this overhead." Well someone with an older gen GPU performs better than my new pro card. The overhead is (as J.P. Owens stated) in their scheme/implementation. Either that or their competition has magical code which doesn't experience these limitations.