First off if I were a betting manI would bet that XTP's have killed more muzzle loader shot deer than any other bullet on the market requireing a sabot.
I used Xtp's in the 44cal. and the 45cal. size for years and never experinced a problem with them.
I have recovered hundreds of them from my sand filled bullet stop and found every one to have expanded despite sheding the jacket. A hunk of lead still kills with out a jacket, many are called round balls some conicals.

As far as the long distance shooting they would work as well as any thing on the market today for that. Biggest limiting factor is the shooter. I was talkiing to my BIL just yesterday about that long distance shooting. He has to either come to my home range or drive to onlytwo sactioned ranges we know of in Michigan over 100 yards.
Sort of hard to figure rise and fall of your load over that distance unless you have a corny to figure out your loads billistices.

If you want a bonded bullet the Speer Gold Dots are still resonably priced bought in bulk.

Al