I just played one of these tonight and did pretty well. The tourney had 4289 entrants and I came out in 224th. I was doing well until I went all-in with AA55x against a player with a smaller chip stack. He had flopped an A high straight, and I didn't hit any cards to make a boat on the turn or river. I doubled him up and lost my stack down to about 8,000. With blinds at 400/800, $50 ante, I didn't have much time to make anything happen, and lost on pocket 2s.
I'm encouraged by how far I got, though. 95th percentile is not too shabby.
