Your discrete card won't work with cutting edge. nVidia optimus (what your laptop uses to combine discrete and integrated) doesn't support OpenGL properly. Configure your laptop to use the integrated graphics for osu! and it should run more smoothly, albeit most likely not quite at 400fps.Well, after switching to integrated, I did get some frame rate improvements, though they are still under 240 if I have anything beyond a static background. This may simply be due to the poor quality of my integrated graphics.
The issue is that I am still suffering from what I presume to be the aforementioned input lag(?) on my cursor, as well as the random frame drops/lagspikes, which are seemingly occurring with the same frequency.