Custom monitor resolutions under OSX 10.8.2?

This is NOT a cable issue! Go somewhere else if you even think of this! ^_^

The DISPLAYS panel under 10.8.2 (Mac mini Late 2012 i7 2.7Ghz) is not providing valid display sizes for an HDMI connected monitor (which is 1680x1050). In fact all selections have the wrong ratios, and ALL selections look terrible (blurry, flickering, stretched, etc.).

Best for display selects a very low density 3:4 (very stretched and looks like it's got a terminal case of JPEG artifacting), whatever it is, it's displaying lower than 720p.

Scaled provides several selections, all look bad, and only 720p and 1080p come close to the proper resolution, but both are very blurry, and 1080p flickers fiercely.

I'm hoping that manually adding (even if it requires editing resources) the proper pixel size, will allow this to display properly.

And if adding a custom size is not possible, "is there an app for that?"

And since when did NOT showing the monitor density become a smart thing?