Baseline (Widescreen) Solution & Issues
Native support. From the Options, Video menu select Widescreen Aspect then pick your resolution.
The .ini edit described below is however necessary for:
1280x768
1360x768 (1366x768 is natively supported)
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Eyefinity / Surround Specific Solution & Issues
In fullscreen mode, the FOV is always based on your desktop resolution.
However multi-monitor resolutions are not available in-game, so a .ini edit is required:
Documents\My Games\insane2\user_config.cfg
seta r_height "xxx" //where xxx is your display height
seta r_width "yyy" //where yyy is your display width
4k UHD Specific Solution & Issues