Oh yeh, it was roycruse, apologies for confusing him with Hugh Jardon.
What part in the rpm range should you look at the slip?
The slip figure is not too important if the boat is performing well but it does give an indication of the load the prop is under. Given that your boat is fairly chunky and has a steep deadrise your 47mph isn't unreasonable as a top speed. Your 16"dia prop with help drive it well but you'll never reach anywhere near 2% slip. If all your figures are correct then the tacho has to be reading low so your 5400rpm will be inaccurate and your revs will be higher.
My previous boat was a 6.5mtr, 200hp and quite heavy. It did 50mph with a low fuel load and about 45ish when loaded so it is fairly comparable to yours. It had a slip of about 18% at cruising speed - around 40mph.