Hello ashepherd, I don't know the answer to your question but wanted to share my experience with my Surface Pro i7 and the new port replicator. I purchased my i7 for exactly the reason you stated. I find that this i7 is great for photo editing and use it often when I am out on a photo trek to run Photoshop CS5, Photomatic Pro, and Luminar. I have found this Surface to be half as fast as my i7-6700K desktop in some benchmarking. I edit images from a 12bit 24Mpix camera and the processing time is quick enough that I have never been concerned with it. I may have waited 15 sec but typically only a few seconds. Also, do you know that the i7 has a true 10 bit video system? It looks very nice. I like my port replicator and am glad I have it as I often connect two USB3 SSD's and a wireless mouse. This system is working really well for me.
In case the new Surface Pro is your first experience with a 2k-4k screen you will need to use file properties compatibility "Override high DPI scaling behavior" and Scaling performed by System (Enhanced) to get the apps to have font and icons larger than miniscule. Some apps are updated but older ones just don't like high res screens.
Happy Trails
Steve