Recently I've rolled with a very large guy, he's about 5'10 and weighs around 320-30lbs. I try shooting in on him, but its like shooting in on a rhino and I fail miserably. I can barely even fit my legs around him when he's in my guard, and I feel extremely gassed after about 5 minutes rolling around with him. He hasn't subbed me yet, but he can usually get me on points. How should I approach guys like this? I was thinking about pulling guard immediately, any suggestions?