I have a 1994 525iT with an Auto and the stock 4.10 diff.

I just got offered a job that will require me to commute about 65 miles each way to work.

One option I have is to sell the e34 and pick up a Civic or Metro. But I really would just like to wring out more mileage from the e34.

What I am thinking about is swapping in one of the following:

3.73
3.64
3.23
3.07

I am concerned that the 3.23 and the 3.07 may be just too long and leave me lugging the engine and not overall be the best for fuel efficiency.

Has anyone out there swapped in one of these diffs and seen an increase in mileage?

Thanks in advance for input.