I use ACT! v19 on a Surface Pro 2 and a Surface Pro 4 with acceptable display. The original problems have been addressed. It is worth noting that Microsoft are continuing to make changes in Windows 10 that address the DPI issues relating to older programs.
I use the Surface as a stand-alone system as well as connected to external monitors. Changing ACT! from hires native screen to a larger monitor works well. I use my own layouts and have found that designing for the hires works well and scales or scales down well when going to lower resolution monitors.
I use a work week layout and 5 days works well. It may become a little cramped in the calendar for 7 days layout on the hires screen.
