Hi David,
On that basis print speed of 80mm /sec, jerk speed of 600mm/min = 10mm/sec means that $fn needs to be >= 50.272 so 300 should be more than adequate. Indeed the print head movement is smooth even with pressure advance coefficient set to 0.6. However, I can definitely feel that the filament is being extruded in a jerky manner. It's hard to describe but just gently squeezing the filament between finger and thumb or resting a finger on the extruder gear, it's akin to a vibration and feels like the filament is being fed in a series of short jerky moves rather than a continuous stream. If I set the pressure advance to zero, it feels normal. It's undetectable by eye.
This is all with a single extruder tool btw - mixing ratio of 1.0:0.00:0.00:0.00:0.00.