I see questions on this forum all the time regarding top speeds and gearing. I've also read a fair amount of anecdotal misinformation on here too which certainly doesn’t help the OP.

Data is king in this regard so I always try to point people to the following link; credit goes to Chris Gamlin - it's an invaluable tool!
Gear Ratio Calculator

It doesn't contain many of the newer or less common bike engines but being an Excel spreadsheet I'm sure that if the ratios were obtained for any given motor (either from the Haynes or the www) then its intuitive enough for most folk to insert the ratios relevant to their query.

I've asked Fozzie to make this a sticky as I think it is likely to save a lot of people time.

Cheers

TC