I didn't say you should expect not to finish, I said you shouldn't just do races you expect to finish. There should be an element of unknown in these things, if there isn't there where's the challenge? If you don't push your limits and court failure then how are you supposed to know where those limits are?
I'm not saying you all out every race but certainly you should be signing up to races where there's a real risk of failure. Personally I don't see failing because something was beyond my reach now as necessarily a bad thing, it just makes me want to reach further next time. We should always be reaching for the things just outside our grasp.
PTL is actually probably a bit tougher, shorter course but another 2500m in height gain and loss, course isn't marked so self navigation is an issue particularly when sleep deprived and the course designers take particular pleasure is marking the way points so that there are a choice of routes between points. All in all a tough prospect.