really dont see the point, 270 lbs on your chest is restricting your breathing and abs done properly requires breathing during the set. The large plates limit your range of motion, and on top of that the abs are not large muscles made to move 300 lbs on top of your bodyweight. You would be better off doing sets of 20 reps with your bodyweight or hands next to your head. Not trying to steal your thunder here, but it looks like mistake getting into those.