@Lord-Grey thanks for the hint to explore the refresh rate, which made me interestingly confused and led me to a better solution. Still dirty though.
besides that, i missed and mixed sth. The listener is eating up the CPU when started but not fed on both versions (LED-FX not connected),
but only with my modified one the CPU usage goes down but with higher refresh rate from LED-FX.
in data:
LED-FX, CPU Load @RPi1
refresh-rate, Listener, Listener_maxFPS100
10, 100%, 90%,
30, 100%, 80%,
60, 100%, 70%,
90, 100%, 55%,
120, 100%, 55%,
same song and effect of course.
Not sure how this works in particular, but it does in sync and smooth (on refresh rate 60+).
My guess is something around UDPSock.recvfrom(4500) is going wild especially while nothing is send to, but i am not that into python networking (and no time to get into) to know and for now i am okish with my solution till sbdy will fix this at the source.