This may help i made a little spreadsheet to calculate speed vs rpm with different gearbox ratios and final drive options. It factors in tyre size will plot speed at a given rpm (but default every 1k rpm up to 6k rpm) and a separate bit for max speed
https://docs.google.com/spreadsheets...it?usp=sharing
its open to anyone to edit so make a copy if its any use.
anything in red is to be edited as needed and i think i have the maths correct if someone doesn't mind checking it over and if its useful take a copy.
Dan