We just got our first Surface Pro 4 tablet in. I'm working on testing it now. For the moment, I have it docked and connected to two 19" monitors. The desktop is extended across all 3 screens. I have the "Change the size of text, apps, and other items" settings as follows:

Surface Screen: 250%
Monitor 1: 100%
Monitor 2: 100%

Everything looks pretty good. But, when I launch a particular application (our core POS software) it goes crazy. This software won't work with anything other than 100% DPI settings. If you have it set any higher, things run off the edge of the window. But even on main two mounted monitors, everything runs off the edge. Never had this problem with Windows 7. We would just set DPI to 100% and it worked great. Any ideas?