I wouldn't shed too many tears. I love my Sabatti in .470 NE, but even if strong enough there is no way you would want a .577 or .600 built on the standard Sabatti frame, unless you were ready to make significant modifications. Sabatti apparently uses the same action for all its deluxe double rifles in .375 and up and the guns just get lighter and lighter the bigger the bore/chamber size, pretty much the exact opposite of what you want. My .470 weighs in at 9lb 10 oz and I was quoted 9lb 6oz for the .500. In the Sabatti your best bet is probably a .450 or smaller, which should tip the scales at 10lb plus, unless you are willing to add weight and a much better recoil pad. Although a little unsightly I use a Kick-Eez rubber slip-on pad and it at least makes an hour at the range bearable.

I can only imagine how hard an even lighter .500, .577 or .600 would hit, on both ends...