Thanks for the feedback, I just tried the game on a laptop with a smaller screen and with less power and hit some of the same problems.
I think part of the problem is that I created the UI for my system so used a stupidly high resolution for the game. I need to build to a smaller resolution that can then be expanded or do multiple resolutions and scale to fit. The stuttering in later levels is probably a bug, I didn't optimize the models for the asteroids they are probably far more complex than they needed to be, the technique I used to generate them in blender looks good but is a bit polygon intensive. I think stuttering is when there are too many objects on the screen.