Yes it makes a big difference, think about how much your slipper & layshaft assembly weighs and how far out the mass is from the center of the shaft!
I think you might well be surprised at how little weight has been added to the RudeBits prop shaft.
I can assure you that the amount that has been used would have been accurately calculated based on a lot of parameters and that Dave wouldn't have just plucked a value out of the air! I am afraid that is all I will be drawn into saying about the DB1 transmission as I mustn't give the game away, ask Tony for the rest ... good luck getting the secrets