Can you try closing all background processes and see whether the issues persist? I also have a GTX 780Ti but experience none of your issues when closing other programs.
Two specific programs that come to my mind are f.lux causing stutters once every second and Teamspeak 3 effectively limiting osu! to 60 fps while it is not minimized (I run things on a 144hz screen).
Two specific programs that come to my mind are f.lux causing stutters once every second and Teamspeak 3 effectively limiting osu! to 60 fps while it is not minimized (I run things on a 144hz screen).