I think I can safely say that it is is no way your monitor that is the problem. The problem is that Geforce 210 video card you have. That card even when it was new was the lowest of the low end, and not much faster than what was available from Intel for integrated graphics. It was also never really made for gaming, more of a low cost HTPC option than anything.
You want to stop FPS drops and slowdowns, you're going to have to get a better video card.