Our 220 lb heavyweight beat a 270 pounder tonight. He used an outside single (exploiting his better quickness) for takedowns. He then cut him, and took him down again. In the second period, the 270 was sucking wind, our guy took him down, put in a half, and pinned him. When you are wrestling guys a lot bigger than you, the biggest trick is to stay out from underneath. (Duh!)
If you are that good at switches, when they get the choice and choose top (big heavies always will - they want to get that weight working for them) switch them out, ride as long as you can, then cut them and take them down again.