OK so should anyone encounter the same:
Changing from opengl to sdl2 did resolve that last issue.
A Pentium G3258 at 3.2 Ghz has some speed issues, but it works fine with 4.6 and up.
Skylake or newer Processors should do with less frequency.
Please do not post a support request without first reading and following the advice in https://retropie.org.uk/forum/topic/3/read-this-first