Hi Tom,
It would appear from the information posted on their site that Brian may owe you if not an apology, at least a concession that you are right in many instances.
I looked at all the figures for GM, Dodge and Ford trucks, and in most cases, they indicate a mileage percentage increase at or almost at the ratio percentage change. In a few cases where the final drive ratio is already at the low end they also indicate much less of an increase.
It just goes to show that many vehicles are not optimized for best mileage, even in these days of high priced fuel.
I do suspect that vehicles with less surplus horsepower and torque will show less of a gain, and that it would be quite possible to overdo the principle to the point that there would even be a mileage drop.

Regards,

__________________
Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C