If you are only going to be working with PS/LR without a host of other apps running, I doubt you see any benefit from dual 8-cores. (That is, isn't it possible that the OS splits up the work between CPUs without the app being aware of it?) However, knowing next to nothing about those enhancements, I guess it could be possible that improvements effect the performance of all app regardless of wether they have been re-coded to specifically take advantage of multiple cpus. PS) have to be coded to take advantage of Snow Leopard enhancements. I assume it only helps with the operating system (e.g. However, I am still left wondering if Snow Leopard has any baring on this discussion since it is supposed to be optimized for multiple processors.

Sounds like if I do, the single CPU route will get me a little more performance, and of course, the better video card. The older Mac Pro works pretty well, but is sluggish. Having extensively used a iMac and older Mac Pro I can safely saw that iMac doesn't really cut for pro-sumer grade photo processing (in my case, 21 mg raw files, lightroom and photoshop).

4 core vs 8 core mac pro