I honestly can't say it would change much. Shardplate is power armor, you're not literally getting stronger, as the case is for pewter, it's more like the shardplate is doing the lifting for you. Adolin and Dalinar are about the same strength-wise in shardplate, despite being dramatically different in strengths otherwise. Pewter doubles, or triple a person's natural strength, which shouldn't change much as far as strength goes. I'll say, however, that burning pewter while in shardplate isn't a bad idea, it improves your endurance and reflexes, which probably isn't artificially limited like strength is.