There can be 3 mph difference between 10 different identical hulls.
There can be 3 mph difference between 10 different identical props.
There can be 3 mph difference between 10 different identical motors.
So you could see 9mph difference between 2 identical boats.
It doesn't make any difference what anyone else is running. Setting you boat up will be different. Motor height, load, elevation, etc all play into this. Make sure you are getting full pull on your throttle/hot foot.
Also, Don't believe everything you read on the net or hear at the docks.