I always rotate the tire one revolution and count how many revolutions the pinion yoke makes.

The 4.10 will increase your rpm's at 65 a bunch, your gas mileage will most likely go down, but it will be a lot more fun off the line. I think gm had a 3.42 gear ratio, that or even a 3.73 would be fine, the 3.42 would be my choice for a car that gets driven a lot. Add a posi trac too.