I understand that I am very late to this discussion, Recently discovered my love for the cosmere
Anyways, seems to me like the effects of compounding pewter would be enormous. It is stated in "The Well of Ascension" by Ham that burning pewter enhances ones own strength, and thus if two pewter arms were both flaring their pewter that it would essentially negate the effects of the allomancy. We see in the same book that sazed becomes near the size of one of the larger koloss, and is able to crush skulls and many other bones with shear muscle, I'm sure you all remember that bit quite well, it was fairly gruesome. Now imagine being able to have that strength for nigh unlimited amounts of time, and then enhance that strength with allomantically burning pewter, any health concerns with the level of strength achieved by sazed, witch apear to be none, would be negated by allomancy, and the strength would almost double, you would basically be the hulk