Well,
It is not exactly an apples to apples comparison, but the old load for a 45-70 was a 45 cal bullet, usually in the 350 to 450 grain range, over 60 to 70 grains of real black powder (the range variances with the poweder loadswas due to differing case constructions, some of the older brass had thinner brass in the base due to the construction techniques and therefore held more powder, new cases tend to have much thicker brass, especially in the base and have less volume).
This load was used on Buffalo from close to some pretty extreme distances.
I would say that your load of 70 grains of pyrodex and a 370 grain maxi would be very similar to these old 45-70 loads and their performance. Pleanty for whitetail at 100 yards.
Just my view.
Hank