The curving and image distortion has more to do with the different refresh rate frequencies, and nothing to do with your monitor not supporting them. If your monitor did not support a frequency or resolution, then it would not display a picture - at all. It would give you an "out of range" error message.
Monitors has required different calibrations for refresh rates @ any resolution since the beginning of time. If your video card does not support a resolution or refresh rate, it would likely not even display in the program options anywhere, and I doubt any software these days would just blindly try to force a specific mode, unless the user set it up that way. Recalibrating is just a fact of life. Changing your refresh rate back to what it was before, will give you the picture you were used to.