Hay Hammerman: That's my favorite lever action, the winchester Big Bore. Mine is in 444 and I shoot the stuffing outta it evey chance I get.
You are correct about the design strength of the Big Bore - it was made to handle those higher pressure cartridges and will hold up to consistent use in those calibers. That's what it was designed for. I load my 444s right up to snuff, but within safe pressure limits. If you don't reload, your rifle will handle any factory production round, which must remian within SAAMI pressure limits for that cartridge. If you reload, just stay within those safty limits and you will do fine, and possibly even better than with factory loads.
I've heard some stories about the Winnes coming apart but have not heard why. You can abuse any rifle, lever or not, and have it come apart on you if you are careless, but the Winnies were made to handle those cartridges, regardless of what some of the 'old salts' say.
As for me, CDNN has the Big Bore in 444 with a 20" barrel and full length magazine tube for $299. I'm calling my dealer to get another one. This be Mikey and I hope this helps.