[GuidoK]

you can calculate it easily from your data:

3244 in 5th gear. 5th gear has 1:1 ratio.
With the 4,10 diff your wheels are turning 3244/1/4,10=791,22rpm

Your tire circumference is 80,36", which means 788,45 revs/mile (1 mile is 63360")
So in 1 min you travel 791,22/788,45 mile, so in 1 hour thats (791,22/788,45)*60=60,21mph if you have the 1:4,10 diff

But you're writing you were doing 70.
So 60.21/70*4,10=3.53
So calculated you have a 1:3,54 diff. Thats a heck more closer to the stock diff. (its not even inbetween the stock diff and the 4.10 diff)
Variations in the calculation are your measured speed (did you use gps? or speedo), and tire wear (tyre wear can go up to 8mm or so, so 16mm in diameter)

4th gear is 1,23:1 and 3rd is 1,67:1 so you can now calculate it for those gears.
But I think somethings fishy here, your rpm spacing is not correct I believe? Are you sure your data is correspondant to the gears you give?
If you do the calculations with 4th and 3rd gear you get different values, which is, of course, impossible.