Do you mean the least amount of weight you take out of a bat? Depends on lots of variables mate I suppose. How heavy that bat is to begin with, the players ability, fitness level, strength, opposition, balance of the bat etc etc.
My main point was, that I really think people obsess over scale/bat weight too much personally and it generally isn't an oz or so on a bat which will make all the difference. I've used a bat which I've scored a ton with and then struggled with it the following week (better attack, worse deck etc). So obviously not the bat is it?
Everyone's looking for the key which will unlock everything in an instant. The bats easy to change, amend etc. Much easier than getting better, fitter or working harder. I see it so much. Had a bloke once who I'd made a 2lb 7oz bat for. He'd been out LBW a few times and his overseas reckons it was due to his bat being too heavy. He wanted an oz out of it, so I did it as who am I to argue, it's his bat. Guess how he was out the following wknd?! 😆
As for the pro's, I'm not so sure they use bats much lighter than we do on the whole. They're just fitter, stronger, better etc. Seems to be a pattern here maybe?