Yeah you can just delete the 4096x2160 from the EDID using Custom Resolution Utility. Make sure you delete it from both "HDMI support" and "TV resolutions" sections.Yep at 60hz it reports 3840x2160 just fine. And before the GPU upgrade and firmware upgrade it worked just fine at 120hz.
Doing it through Windows gives the same result at >60hz (and Windows even shows "active signal 4096x2160"...).
Did a clean video drivers install, reboot, and plugged into a different HDMI port on the GPU and still no go. I'll try a different HDMI port on the TV too. edit: didn't help
Could I just edit the EDID and get rid of this useless 4096x2160 res maybe? I'm a little scared of breaking something. Wish I could just downgrade the firmware but to my knowledge that is not an option.
Edit 2 : OK it's some nvidia scaling bug. I have to use aspect ratio/display AFTER switching to 120hz to fix it.
Means integer scaling is not usable for me at >60hz for now. Well I don't exactly need it right now but this is a really silly bug.