Zantetsu
Smash Master
Okay, so my original test was flawed. I had tweaked around with Ownasaurus' build a lot before trying your file out, and I think that messed with my results, because when I downloaded a fresh build to use your .exe with, I got different results. Both disabling the audio sync in Jabos and switching to the old Azimer's plugin fixed the 58 fps issue. Neither of these options seemed to work with the original .exe, so whatever you did appears to have solved it.It just occured to me that maybe the 58 fps issue is due to the audio plugin. Be sure to disable audio sync in the audio plugin settings too. If that doesn't fix it, I guess I'll have to try it myself and see what's going on.
Edit: Just tried connecting to myself and I had 60 fps. I beat story mode and never desynced.
I still have yet to do some sync tests, I don't have my spare PC on me to do so. I'm concerned about desyncs because Ownasaurus specifically said "to allow for full sync on kaillera, core runs at ~58 VI/sec instead of 60 VI/sec" which makes me believe he made that limit for a specific reason, and removing it might cause it to desync often. However, you claim to have tested it without any desyncs yourself. When you did test, were you using Jabos audio plugin or did you switch it to an old one like Azimer's? Being able to use Jabos audio over Azimers would be a huge incentive, since Azimers has a large amount of delay to it.
Also, I'm assuming the fullscreen issue hasn't been touched (yet?)? Going fullscreen in a netplay session by myself caused my end to be paused during the fullscreen, so I imagine it still causes a desync.