You always get more holding power by adding surface area, more clutches. Different manufacturers make different thickness clutches and steels. Many make specialty clutch steel combinations to increase holding power in drums. Many rebuilders have lots of different clutches laying around, as long as the clearances are correct stack as many as you can get in the drum. If you bought a stock trans kit, you will most likely only get 4 clutches in the pack. If you want more you will have to buy a different clutch and steel.