The fastest I have ever been on a SeaDoo was 64 MPH on radar (we didn't have GPS in the 90's) which in itself doesn't seem like an impossible feat, but the special part about it was that it was 1993 when we did it and it was on a 91 SP.
It was a converted 580 snowmobile engine with RAVE, long before the 787 engine was available, had no rev limiter and a prop from a 93 XP. We built the boat to race in the IJSBA courses, but it was disqualified for obvious reasons. It also had the massive sponsons from a GTX, which made the boat turn at a rate that nearly tossed the rider. We were never sure about what RPMs it turned, but it was much higher than the mid 6000's the machine was used to.
It only ran on race fuel and it only logged 110 minutes of use before it overheated badly, melting the custom exhaust outlet and sinking at the boat launch. We pulled it out with a suburban until we could winch it on a trailer.
And wouldn't you know it? 2 years later the XP800 was available with RAVE.
No, it was not my idea, I cannot take credit for that part.