May be you should check the following link before you make the decision.
http://pindelski.org/Photography/2013/10/23/new-mac-pro/
The new Mac Pro is a beautiful machine, but it is so Final Cut Pro orientated. Almost no other software can take full benefit from that machine. For photographer, I think the oMP is still the best choice, better expandability, more or less the same performance with only 1/3 of the nMP's price. Able to run 24/7 but still cool, quiet, and reliable.
Of course, if you need mobility, the oMP will not be your cup of tea (the nMP is actually considered portable, but just not able to run like a laptop). Therefore, if you need both performance and a portable computer, And a 24/7 machine, the nMP should be the best choice (the most expensive one as well).
In terms of performance, the MBP's spec looks pretty good, or matched with the desktop. However, the thermal throttling will make it never run as fast as the desktop. Of course, it should still be enough for normal photoshop operation. But as you said 16G of RAM may cause you trouble later on. An SSD scratch disk will help a bit, but still far slower than the RAM.