How to cook large quantities of Boston pork butt

100°C for 7 hours sounds just about perfect. The meat will be meltingly tender by then. In fact I think you could go even lower on the temperature if you like, say 80°C or 90°C. Of course, if you want to be absolutely sure, check with the thermometer, but unless you know that your oven is unreliable or you happen to be in possession of the largest pig shoulder in the world I am 100% sure it will be more than done in 7 hours on 100°C. Good luck!

I don't think a pork sirloin roast will stand up to that kind of cooking very well. That is a very lean piece of meat, which does not lend itself to long cooking times at low temperatures. That type of cooking is best reserved for cuts of meat with lots of fat and/or connective tissue. If you put a pork sirloin roast in your cooker for 8 hours on low, you're going to have one tough, dry piece of meat when you are through.

You would be better served by cooking it in the oven at higher heat, for a relatively short period of time, like 400F for an hour or so. Bear in mind, you're not going to get to a fall-apart tender state with a sirloin roast. This isn't a pork butt with which you're dealing, which you'd take up to an internal temperature of 195F or more. Rather, you're going to want to target the safe temperature, and no higher. You want the meat to be juicy. Cut into thinner slices to achieve maximum tenderness.