I think that you are going to find out that heavier is better - either way. My poodle shooter destroys 55 gr FMJ bullets at the velocity I push them using a 1:7 twist.

Those 77gr SMKs Mapper mentions, in my 16" CMMG 1:7 will put those baby bullets in an eyeball size hole all day long at 200 yards. And I believe the group is that big only because my optic has a 1MOA dot.