Gears: Can you really knock off 9 tenths?? "ET GUESSES"

[Dark_5.0]

One of the salesman for the company that I work for who also builds race car engines told me that some of the cars that he has worked on have dropped 9 tenths in the quarter with a simple gear swap.

I was expecting to knock off about 5-7 tenths in the quarter after my gear swap from 2.73's to 3.73's.

This will be the first "major" mod that I have done to my car and I cant wait to see how much it helps, also after the gear swap should I run more MPH than I am now?

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88 mustang gt convertible bored to 306 BBk equal length headers mac cold air fender kit cowl hood nitto drag radials ford racing clutch flow masters h-pipe 160* thermostat 16 degrees of timing electric fan off 94' t-bird jacobs electronics cap and wires. Edelbrock 1 1/2 inch drop springs.
best 60 ft 2.14, best 1/8th 9.65, best 1/4 15.2 @89mph, Stock gears and 3000+ Altitude