One of the fundamental print speed issues is the extruder flow rate, a variable aperture nozzle could in theory help and changing nozzles, but fundamentally if you can increase the flow rate you can increase the print speed.

So could we detail the limitations to increased flow rate here, which may help maximise the potential of the system.

If this works can we make this thread sticky and in future add to the wiki?

another maximum is how fast you can heat the filament to temp equilibrium. Faster flow rates might need a larger melt zone inside the hot end in order to have sufficient melted plastic in the reservoir. But a larger melt zone will probably also make retraction a problem, leading to more ooze, but if the head is moving fast enough it might not be

another max speed limiter would be how quickly a build dissipates heat, and how long you have to wait for each layer to cool, but this can be sped up by a fan.

Here's a printer doing 300 mm/s with PLA:
[blog.ultimaker.com]

Damn!!

My 20x20x10 test print with 20% infill was 1/3rd done when I started watching it, and is only finishing as I type this!!

I will need to up my speed lol