ok just done some reading up on it (sh*t im bored) and it seems the box oil used can be a very slight factor. too frictionless an oil and the time taken for the gears to spin up to the right speed to allow change is increased. also something about "shear rates"? however, it is also meantioned that this may not have any noticeable difference on trans. loss. A straight cut box will reduce it, but is very expensive and often not cost-power effective.