The highest gearing I ever ran, which was in USVTA, was 55/37.
With a front spool the torque was easily noticed and pull out of the turns is awesome. If you are still using a front ball diff I think that the advantage of shaft drive is diminished, which I noticed when I went back to the diff after blowing up a set of steel universals on the spool. If you can get a front diff in the thing with 100K weight in it that it would be pretty sweet.