79T will hit 13k quicker. 66T will yield a higher top speed.
There is a formula which I am the last person to ask ask about it! But with a 16/70 my friend figured it was 95mph.
Larry, it took me all of 5 seconds to look this up on the internet, maybe you could do a search and figure these things out yourself.
Anyway, here is how to calculate gearing and speed.
http://www.csgnetwork.com/kartpotentialspeedcalc.html
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