I'd be content with .650-.700 if there are occasional special years (0-1 loss). I don't buy the level of competition argument. Don't we all want BYU to be considered a top team? If so, win at the same clip and knock the big dogs off once in a while.
I agree BYU plays and wins on over-achieving, well-schemed, lesser-talented athletes. I don't want to call it a ceiling, but I'd say it's at upper end of potential.