Ok, solution found. The clue was in reading the report on the current resolution of my monitor as 1536x864 despite the fact that Nvidia control panel and Windows were listing me as being at 1920 x 1080.
I had also noticed that my text seemed slightly blurry after changing to windows 10 but had no idea why.
Research on that 1536x864 resolution reveals an issue where updating to Windows 8 or 10 can enable by default a display scaling of 125% to enlarge icons for better readability (useful for tiny laptop screens with high resolutions) which is why Windows thinks it's at its native resolution of 1080. However, GeForce Experience is unaware of this change and displays the resolution at something lower to adapt to the scaling.
The solution is to go to Control panel (In windows 10) then "appearance" and "personalization" then "display" and select "set a custom scaling level" at that point, set the level at 100% and Outerra menu's now work correctly.
No other program I use but Outerra experienced problems with this, so maybe something can be done on the Outerra side to compensate automatically as well?
More on the issue:
http://www.tenforums.com/tutorials/5990-dpi-scaling-level-displays-change-windows-10-a.htmlCameni, Windows 10 is apparently reporting incorrect display information deliberately
http://www.infoworld.com/article/2952506/microsoft-windows/high-resolution-displays-reveal-windows-10-blind-spot.html