@simulant
Thats a combination of flaws in the gfx driver (i think) and screenmode prefs (i'm sure of)
Take a look
here
The consensus is that you need to manually alter your gfx settings in your Monitor file.
(System:Devs/Monitors/Your-Monitor-file)
I finally ended up leaving the @60 on my 2560x1440 mode and simply adding to the max kHz the monitor can handle.
I have a BenQ BL3200 which is specced at 88 kHz max in the Horizontal Frequency.
If i use that setting my 2560x1440 mode won't ever show up because it's considered "out of range" (when using it with @60 and since Screenmode Prefs ALWAYS uses a minimum of @60 it will ALWAYS be "out of range").
The same gfx card on the same monitor works perfectly fine with that mode in a PeeCee.
So, after playing around a long time i finally decided to simply add 2 kHz to the Horizontal Frequency of my montior and et voila, 2560x1440@60 is working.
Monitor is still not burning, hissing or displaying any other odd things after months of use.
I guess the companies spec their hardware to a "safe" range and PeeCee drivers simply step over that range to reach their goal/mode.
Screenmode Prefs is buggy and it seems the gfx driver is restrictive enough to not let that happen.
Good luck
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