Those two technically are not exclusive. Apple's SSDs are proprietary (made exclusively for Apple ). However, that doesn't mean a 3rd party can't but another custom design in the same socket.
These two stories aren't 100% consistent... but it is CES floor show talk and a future product so perhaps not too surprising.
http://www.thessdreview.com/daily-n...n-ssd-upgrade-capable-1-8gbs-ces-2013-update/
http://www.anandtech.com/show/7673/owc-to-bring-aftermarket-sf3700-pcie-ssd-upgrades-to-2013-macs
Q2 or Q3 .... It wouldn't be surprising if it is Q3 and they wait to see if Apple doesn't tweak the connector or do something silly. Or deviates into standard M.2 format ( which would be sensible). Either way it is going to be several months before there are any options here.
Some folks don't like LSI/Sandforce Flash controllers. The 3700 is a new generation so the vast majority of the 'haters' don't have any real world experience with it.
Doubtful these are going to be dramatically cheaper than Apple's. If faster than Apple's then OWC will probably 'lean' on that factor to offer at approximately the same price. [ in part to offset having to custom engineer to Apple's tweak of M.2 ]
For that workload the D700 is overkill. If know for sure going past 16GB in the short-medium term then tweaking base model for 1650 (6 core) and D500 is a bit cheaper. Short term have 12GB but only have to unload (or keep for back-up) 3 DIMMs instead of 4.
A D500 adds a small amount of longer term upside if LR+CC evolve in next 2 years to do more GPGPU workload. Not sure what kind of coding but D500 is also likely an incrementally better match to future libraries/contexts.
If intent to keep the Mac Pro for over 4+ years then probably a better move.
If intend to stick with CS6 for next 4+ years then D300s are fine.
Not sure what you are doing with Mini after retirement, but one option is to pulled the 1TB SDD from mini , insert into a TB enclosure , and attach to Mac Pro. Can use the standard config's SSD for OS/Apss and continue to use this 1TB for you archive.
If 80+% of the content of this 1TB SSD is compressed pictures then the then LSI/Sanforce 3700 may/may not be a good choice. It should have incremental refinements for handling compressed data, but if primarily just have 100's of GB of compressed data to store those are not the best match for a flash controller. They are aimed at much more "normally balanced" data sets.
Whether six cores is going to help is highly dependent upon the editing actions you invoke. Again if on the CS6 "forever" bandwagon then the current "rule of thumb" of 6 core being sweet spot has more traction.
If going to track software maximizing available hardware then 4 core may be more viable than old rules of thumb suggest.
Is your intent to upgrade machines with same/similar period frequency as the lease length? 2-3 years and upgrade is likely the pace you'll be on.
If targeting a 4-6 year cycles it is a mismatch.
Whether it makes sense tax wise is probably a better question for accountants than this forum. It is really highly dependent upon your specific revenue stream (both amount and how consistent it is) and costs.
