You can grind as much or as little meat together as you'd like, using equal parts of each type. Martha made this recipe on Cooking School episode 407.
Cut both steaks into small pieces. Grind through the large holes of a meat grinder. Combine in a bowl, then grind together through small holes of grinder. Divide into 4 equal parts (each about 5 1/2 ounces). Form into patties, each about 3 1/2 inches in diameter.
Preheat grill to medium-high. Season both sides of burgers with salt. Grill 2 1/2 minutes a side for medium-rare, placing cheese on burgers in last minute. Transfer to a plate. Grill rolls until toasted, 30 seconds. Sandwich burgers on rolls with pickles and ketchup-mayonnaise.