Nearly all of the fields in my area are 1/4 mile from ditch to ditch, so it is very easy to tell a distance by counting the fields you pass.
I have a 2001 F/liner  370 Cummins w/ 10 speed OD, 3.70 rears, and lo-pro 22.5's. 
I judge how heavy my load is by the distance it takes me to get up to 50 mph. as I come out of the field on paved roads. I am running 8 mph as I leave the field.
3/4 mile to reach 50 mph, less then 80,000. More than 3/4 mile, over 80,000. Just an approximation, but fairly accurate.