Probably Windows 7 quirks. If you swap the 290 to the Windows 10 system does it work?
EDIT: And yeah, using the scaling setting is a better choice than outputting a non-native resolution. Programs using standard GUI APIs will look the same, but those that are HiDPI aware will be able to take advantage and render 3840x2160 but with the sizing of 3200x1800. The only downside is that programs using custom GUI toolkits that don't support it will be 3840x2160 native sizing, and with the increasing popularity of HiDPI screens they're growing smaller in number.