Mozzzaaa
I have the exact same requirements, here are my findings based on some observations from Activity Monitor and research based on how the hardware works.
Photoshop does not utilize multiple cores well for many standard editing ativities - therefore one core will be busy while the rest remain idle, however I have noticed over time that upgrades to Photoshop seem to take more advantage of multiple cores as Adobe updates the code. For example, appling filters utilize all of the cores while the filters are computing changes (smart sharpen for example). Try running CPU monitoring in Activity Monitor (double click the CPU graph to display all cores).
Lightroom utilizes all of the cores for Import, export and other activities that process multiple files. Being more modern code, it beter utilizes muti cores.
Keep in mind that each core handles two code threads, therefore a four core system is capable of processing 8 "streams" of code, the 6 core can manage 12 threads, etc.
Here is a screen shot of Mac Book Pro running PS CC Smart Sharpen:

All the new Mac Pro run at 3.9Hz Turbo Boost - they are all the same in that respect. This means that when the processers are not hot, at least one core will run at 3.9Hz - therefore on a relativly idle machine (just editing in PS for example) you would likley be running at 3.9Hz on all the Mac Pro 2013.
There are also the GPUs to consider. Apple as usual has not made enough information available to easly determine the cost benefits of the more powerful GPUs and I don't know if PS would utiliize the AMD GPUs well now, or perhaps better utilize them for the future. Perhaps someone could comment on that. Here is an interesting article: http://architosh.com/2013/10/the-mac-pro-so-whats-a-d300-d500-and-d700-anyway-we -have-answers/
Clearly the D500 that is standard with the 6 core seems a major bump over the 4 core D300 (therefore the costs of the 6 core reflect that). I don't know how much the D700 would cost - it would be helpful if this were published so I could consider my order.
There are two GPU in the new Mac Pros - but the purpose of the second one is not toally clear (thanks again to Apples's communication). It likley will be utilized for all sorts of things that don't really exist now and FCP X is scheduled for a new release better utilize the GPU for video (as nwaphoto mentioned video processing will be a major use of this equipment).
I was interested in your comment regarding 64 Meg ram. Yes that would be a hudge boost to PS performance, but would it be better to purchase from Apple or wait for OWC who offer RAM at major discounts over Apple. Once again, no info yet that I am aware of.
I believe the flash drive is upgradable but rumor has it that it uses a proprietary connecter. Makes me want to go with the largest size but once again OWC might be the way to go for an upgrade in a year or two.
In the past, the 6 core 2012 Mac Pro's were somewhat of a sweat spot in terms of horsepower vs cost. I will be considering that in my decession to upgrade. So I am considering a 6 core, will check out the Ram and Flash diIsk based on price - which is the infor I don't have. If you have anything please post
Thanks