I think as long as you ride at a pace you're comfortable with, you will not only finish with no problem but really enjoy it. Maybe you finish with more leftover energy than you expected but that just means go back and ride it again some other time and kick it up a little. When I did my 57 miler, I slept damn well that night. I think I could have gone a little harder but I didn't really know, didn't want to over do, and didn't want to leave my brother behind. We looped around a lake so if we ran out of juice, there was no easy finish. The last 5 miles or so, I gave it everything I had left, I told my brother I was gonna finish it out and see him at the truck. Anyway, before I ramble any more have fun with it and come back & update after the ride.