If any one would bother to check, quite a few old time strongmen did mid 400's to 500 in regular workouts. Herman Goerner was in the mid 600 lb range I believe. Those were mostly the solid cast iron bars (and thicker gripped) or shot loaded globes on the ends of the lifting bars. Not the best balanced in the world. A guy named Cavattone did 562 one handed last year. Do not know his bwt. Experienced strongmen and trainers seem to agree that a lifter should be ably to almost do (with-in a 100lb or so) an equal amount with one hand as with both hands. Seem logical, seeing as how the arm(s) are gripping and hoiding the DL'ing bar in place while the back and lower body does the actual lifting.