I remember creating a new modeline and adding it to the list. Then using ctrl+alt and +/- to cycle through the modes. I would get to the new mode and the monitor would start buzzing and clicking and the image would flicker. I would quickly toggle to the next mode that was "safe" then go back and edit the modeline and try again.

I did manage to get my monitor to run at 1280x1024 @72Hz but couldn't make it go 75Hz