Originally Posted by Stealth ///M
Had 4:10s in my old supercharged car(s). Took them out as went to a
3:73. That tall of gearing is useless in the first two gears. Also, that gearing doesn't increase torque, only multiples the feeling of it in the first three gears.
Going from a 3.85 to a 4.10 in an E9X M3 is very different from going from a 3.62 to a 4.10 in an E46 M3 or a 3.23 to a 3.64 in an E36 M3. It is only about a 5% difference and will not make the first two gears useless. BMW selected the 3.85 as a good compromise between efficiency and performance for the average driver -- it was a compromise.
A differential change will affect the multiplication of torque in all six gears on the 6MT, not just the first three gears. It is true that the additional multiplication offered by the transmission ratios ceases once you reach the 1:1 ratio, but that does not happen until 5th gear on the E9X M3 with 6 speed manual. The overall multiplication obviously does diminish as you go through the gears, but you will feel a diff change in 4th, 5th and 6th.