or are you suggesting I set the game to 60Mhz and 640x480?
That would not guarantee you anything - my old monitor maxed out at 85Hz at 640*480 and many of your customers will have such hardware. On my old monitor, the code that looks fine for me now would look jerky again.
Similarly, if I run your code at 1024*768 AND set TargetFPS# to 85 rather than 60 it looks fine (the FPS counter suggests an update of 42.5 frames a second... fitting exactly with the monitor's optimal speed at that res').
You basically have a couple of questions to address: Are you going to allow your code to run at multiple speeds in order to appear smooth on a range of monitors (remembering that you can still retain some control over the range)? And, if so, how are you going to let your program know what speed it should adopt?