Thanks for the info. Yes, I'm running latest Windows 10 IoT (build 14393) on the Dragonboard but worth checking as you say.
Thanks also about that command line to change res. It doesn't work on the 410c though. Here's what it says:
C:\Data\Users\Administrator\Documents> SetDisplayResolution 1024 600
Set Display Resolution and Orientation
Your device only supports one display resolution
I can't change the existing device resolution settings
The IoT Grove Kit does comes with that 5" (800x480) touchscreen but the kit is to go with a Raspberry Pi, not the Dragonboard 410c unfortunately (https://www.seeedstudio.com/Microsoft-IoT-Grove-Kit-p-2694.html).
I also have an RPi2 and an RPi3 - both work absolutely fine with our 7" touchscreen (1024x600). It's only the Dragonboard 410c that seems unable to adjust its output resolution to anything except 720p. I hope you have some luck with the 800x480 touchscreen when you get it (I have a 800x480 5" OLED TV and the Dragonboard display fits on it - the TV scales the 720p HDMI signal, I assume - but normal size text is unreadable due to this scaling).