A little OT but not really.
I run an original 3.78 diff in the car I tow a camper weighing very nearly as much as the car around Australia with and a 26% Mitchell O/D and a Mitchell synchro gearbox (with 15% higher first and second gears). When towing, the 3.78 is handy on a hills or in towns but on the flat and in O/D, it is fine. I've even taken off from a stop (remember 15% higher first gear) and found I have forgotten to shift out of O/D.
By my calculations, a 3.78 diff with 26% O/D is the same as a diff ratio of 3.00 without O/D. If I can start from a stop with camper in tow with a diff ratio of 3.00, I figure 3.26 would be easy in a solo car. The 15% higher first gear makes my first gear even higher - like having a diff ratio of 2.61.
