Well I just ran these with both of those settings commented out, in hopes of letting them set themselves? That seems to work great.
Sorry it is a bit messy. look at the word “engineering” at the bottom of each letter. There is zero accelerations happening and it is slamming. The difference between them is Junction deviation set to 0.2, 0.016, 0.008, 0.002. There seemed to be zero difference between them. The accels for that in general do not seem right. If you look at the concentric circles, the smallest two run stupid fast, the rest seem to have accels happening.
This test file ran like actual dog poop on 414, almost perfect on the 415. If you run it I have the pen offset the thickness of a paper business card when I hit start.
Arc Torture test.gcode (24.8 KB)
Arc Torture test.zip (20.4 KB)