Ok cool. Learn something new everyday 
What are the numbers? 
I know very little about gearboxes to be honest :embarassed:
The higher the FD number, the lower the gearing, meaning the more torque multiplication you get at the wheels...but the slower you go in each gear - although you go through the revs faster.
Shorter gears = faster acceleration, but slower peak speed in each gear.
Higher revving engine + shorter gears - faster acceleration but the peal speeds remain the same.
For example, a standard car will do 67 MPH in 2nd @7000 revs.
Fit a 3.94 and it becomes 62 MPH @ 7000 revs - but faster through 1st/2nd.
Fit a 4.23 and it becomes 58 MPH @ 7000 revs / 60.1 @ 7300 revs - but even faster through 1st/2nd.