Here's some food for thought. At the PBR Finals, I divided the bulls up into 2 groups using the average power rating (which is a way to measure difficulty) for UTB events (around 73)
The "above average" group
Power rating 73 & up
227 outs
30 qualified rides - 13.2%
Avg. mark: 21.77
The "below average" group
Power rating under 73
58 outs
23 qualified rides - 39.7%
Avg. Mark: 21.51
If you are a bull rider, which group do you want to draw into?