For my monitor resolution issue: Nvidia (Andy) asked me to enable ModeDebug in my /etc/X11/xorg.conf, restart and provide the /var/log/Xorg.0.log which I have done. The log shows that “Mode is rejected: PixelClock (185.6 MHz) too high for Display Device (Max: 165.0 MHz)”
But EDID shows that the the resolution is valid and that the max dotclock is 240 Mhz, so this 165 limit seems to be artificially imposed. This occurs for both of my monitors (HDMI-4 and DP-6).