Based on the following numbers I would support a steep increase in the number of perks for the M4.  The total number of shermans produced in WWII was around 2200 vehicles.  In each British armored platoon on 1 in 4 tanks was a firefly.  Total number of Tigers produced in WWII was 1355 vehicles.  That being I say the perks for a Tiger are sufficent.  However, if you used the vehicle production number as a starting poing for perks then I would say the M4 should start out at no les than 15 perks.  That would be normally half the cost of a Tiger.  In addition, I think there needs to be some change to the damage model.  Like another poster said, I dont know how many times I hit an M4 broadside with shot from a Tiger and nothing happens only to be killed by the M4.  Of course I have adjsuted tactics and started shooting long range.  But something needs to change.
BigKev