For Sunlu at 240°C i had first defects at ~21mm/s. I think i set max speed to 18, but right now it is at 20. Seems i changed and saved that accidently 
I just realized that I didn’t test the IEMAI yet and just set it to 20mm/s 
Somehow that works fine for any of my filaments.
My last tests were inconsistent with the previous ones. On steep overhangs, the Sunlu was even a bit nicer now. Then I printed a part were i put all the settings to use, that I thought I had found and the result was terrible. 
Then I discovered that the Sunlu profile is set to 255 °C instead of 240°C and I have no idea when that happend. So I’m loosing trust in my tests 
But probably, the model was rather stupid. And a benchy at every speed 300, only outer walls 250 turned out very nice. So I’m regaining trust again.
Repeating PA and volumetric speed tests right now. Then i need a benchy with the Sunlu for some positive feelings. And then, I don’t know, probably I should print something useful instead of rounds and rounds of tests
But I fully agree that the printers are really amazing compared to what i did with my Ultimaker. I’m still mesmerized when watching it laying down a top layer at 300. And all the bells and wizzles just working.
On the short perimeters: I think I understand the setting, but I’m lazy to find out how it could improve quality.