I have tried:
50mm/s print speed, infill at 50mm/s, wall speed 25mm/s

and 60mm/s print speed, infill at 60mm/s, wall speed at 30mm/s

both giving the same result.

Other details are:
layer height 0.2mm, line width 0.4mm with a 0.4mm nozzle, 3 walls, 4 top and bottom layers, infill 25% Grid, infill overlap 30%