To clarify, this isn’t a blockage - I have cleared the nozzle/extruder. I actually tested this with the motor and gears detached from the hotend.
If I run an extrude at 10mm/s or 50mm/s the gears move the filament through smoothly - any other speed, the motor sort of clicks and the filament does not move. This behaviour is also shown on the drive shaft from the motor when the extruder gear section is removed.
This one appears to be solved. I fully detached the motor from the printer, checked and cleaned the contacts and reconnected and touch wood it seems to be functioning properly now…