I don't really get gentle break-in periods... Whats the first thing performance engines do after being assembled? Get on a dyno and show what they've got.
Seems to me if you want rings to seat properly you need them to get warm and snuggly with the cylinder walls as soon as possible.
That said... If I were fortunate enough to take ownership of a new 6.4 Jeep, that 500mi break-in period would probably be up before I got home from the dealership