Carefully mix the meats, bread crumbs, steak sauce, eggs, salt, and pepper with the tines of a fork, but do not mash them. Lightly form hamburger patties and press lightly into shape.
Prepare a charcoal or a stove-top grill.
Cook the hamburgers for 4 minutes on 1 side, then turn and cook 3 minutes on the other side for medium-rare. Remove to a plate and cover with aluminum foil. Allow the hamburgers to rest for 5 minutes. Meanwhile, grill the buns, cut side down, for 1 minute, until toasted. Place a hamburger and a slice of blue cheese in each bun, plus arugula and tomato, if desired, and serve hot.