Chiming in here with 3 displays I tested this evening.
Dell Alienware AW2518H (this is the G Sync version)
Only 2x mode works fully here
3x, 4x, and 5x all produce sound but no picture
the AW2518H has no “Display” settings that allow you to change aspect ratio, so you’re stuck with a stretched image in 2x. Extremely disappointed at this displays compatibility.
Oddly enough.. the AW2518HF (which is the Free Sync version) has reports of full compatibility, and this model has “Display” settings in the OSD which contains Aspect Ratio settings
My theory is that, with the AW2518H (G Sync ver.), the panel has to adhere to stricter requirements to be allowed the G-sync badge of honor, and disables settings, and apparently tolerance to video signals.
All modes except 5x supported (5x displays an image.. but it’s really corrupt with pink and green lines)
Eureka! This baby loves the OSSC (thank goodness!)
All modes supported, all timing adjustments displayed a picture
Perfect compatibility from my testing