In my opinion, although some slicers do attempt to handle acceleration, it is still a function that is built into the firmware and best left to the printer to resolve. It is possible to change the printer's maximum acceleration rates via GCode.
The problem with talking about speed as a single entity is that it quite simply it is not something that can be discussed as a stand-alone parameter.
For example (with stupid values), what is the point in trying to print at 1000mm/second at a layer height and line width of 1mm when the extruder can only melt 1mm^3 of filament per second and the maximum acceleration is set to 50mms^-2
All these factors (and a few more) need to be considered as a whole.
I found the communication with E3D regarding the V6:
Printing with a V6 using pure MG94 ABS 1.75mm which we know the characteristics of very well and has a melt flow rate of 11.7g/10 min, running the HotEnd at the normal print temp for this material which is 240C we found the following:
11.5mm^3 per second is the max comfortable flow rate, you can go a little faster but extrusion is not as optimal.
This means an extruder feed rate of 4.8mm a second is easily achievable. These numbers are very conservative and are only a measure of max steady state flow.
Feeding 4.8mm of 1.75mm filament is 11.5mm^3 which will print a line (approximately) 143mm long at layer height of 0.2mm and width of 0.4mm, hence a maximum theoretical limit of 143mm/sec with that filament at those temps, subject to the possible acceleration and settings of the printer.
I hope this helps.
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage or loss.