After all the updates to my Anycubic I3 Mega-S printer I'm now able to print this at 100% size!
Updates on Printer were: TMC2208 Steppers, Marlin 1.1.9 Firmware, new part cooling.
Important parameter for print quality is "Outer walls before Inner walls"
Print took 3hours, post processing 45min.
Added some silicone lubricant finally.
Generic PLA Pla
Print outer walls before Inner walls,
60% concentric support