Following info only relates to latest Pi 3 B+ and retropie 4.4

From the limited dicking around I've been doing it looks like the software revisions by the Retropie crew for 4.4 to run with the newer Pi3 B+ has borked C64 emulation completely, with the default version of VICE i get games running at around 25% speed, totally unplayable. at the same time, Nintendo 64 speed and emulation is best it seems us C64 diehards , long in the tooth as we are, have been forgotten since last year's update for the new Pi3 B+ Hardware.

until an update is released that deals with these VICE speed issues, if you use the retropie setup menu and go to the experimental packages download sectionand look for VICE for Libreto - this runs C64 games perfectly - though it lacks the comprehensive menu options of the full release of VICE, at least it gets you playing games again if you've upgraded and got rid of that old Pi 2.