what would be real number gps speeds with 454 mag efi on this boat?

I had the 1999 22zx with the 7.4 and the best that I seen as honest speeds was 63 to 64 mph and that was in ideal conditions. If you have any other questions that I can help with feel free to ask away.

I've got a 1999, 22ZX, 454 (7.4 MPI) B1, and my GPS reads 63-65 depending on conditions.