I have a 97 Seadoo GSI with 90hp and an engine that you can pitch to give you more speed or more maneuverability. My top speed is around 55mph. A lot depends on the condition of the lake and who you are riding with. Some of the newer models with more hp can do well in excess of 60mph.
challenger boat by seadoo, not a PWC? I know the top PWC's can get close to 70MPH. A friend just got a challenger last weekend, but he's in the break-in period so we didn't get to see top end.