I saw a placard as high as 475 last year, they let everyone in that was post marked on the cutoff IIRC.
They loop you all through the park, some of it is on horse trails and double track. Last year we went through the bike trails 2 times for most of them, on the way out and again on the way back. Some were rode backwards and some the same direction both times. They also do a formal start at 8, but the trails are open at 7:30. Our group usually rolls at 7:30 to avoid the logjam so we can stay together.