Bullet diameter won't make much difference when it comes to leading in my experience. You need to be more aware of the Brinnell hardness of the material the bullet is cast from and of course, maybe even more important the luburicant in the grooves and whether or not there is a gas check.
It's to bad the BB doesn't offer powder coated bullets.
By the way, the owner of Bullet Barn is going through a battle with Cancer. Not sure which type but none of them are good. If you place an order be sure to wish them well and give them your blessing.