http://imgur.com/a/XToZQ so apparently the frame skipping on integrated graphics is white(BetweenFrames) instead of purple(Draw). meaning this problem is definitely not the nvidia card's problem since there's nothing for it to render in that time causing the huge draw times
This is definitely an issue with osu itself, im having a very similar issue and I've been playing everyday for almost 4 years now without any issues, I even factory reset my pc and the issue is still there, so it is not a conflicting program or anything along those lines
Update as of 31 may After messing around with an external display for awhile osu now runs on Nvidia gpu with LOTS of white lines in the fps counter but runs quite smoothly. I still see frame skipping (straight cursor trail during spinners) but osu doesn't micro stutter anymore. Problem not solved but at least the graphics aren't anger jittery and anger inducing anymore
Try to check if there are any spikes in the CPU Usage If it's CPU, you can download [lucky:1337]Process Hacker[/lucky:1337] and open System Information When you lag, hover over the spike and to find the program responsible for the spike.
Click on "System Information" at the top bar Should show up a new window that looks like this Hovering will show the program responsible
I gave up finding a solution long ago. I find restarting osu until I get one that's not really laggy the only thing to do now. Run osu Nope too laggy Restart osu Eventually it will have minimal frame drops
note on Aug 26 stuttering is still as present as ever. CanForceOptimusCompatibility=1 causes osu to crash entirely with the Cannot find the name of Intel ICD OpenGL driver. Setting it to 0 allows osu to run so maybe the devs can look into that