(at such low filler loadings the tungsten will change the modulus of elasticity very little)
petg does have higher yield stress than pure lead (53 megapascals vs. what https://nickelinstitute.org/media/1771/propertiesofsomemetal... says is 17 megapascals) but there are lead alloys that are in the same range of yield stress, including regular lead-tin solder. but they won't last if you try to make change gears out of them precisely because they're harder than petg
by the same token, though, i think you're going to get a lot of springback and long-term distortion out of petg you aren't going to get with lead