O.K. Here is what I have '96 Ebbtide Mystique 21' 5.8L (stock 260 hp) EFI punched once over, CMI Stainless headers thru the hull with muffler tips, and Volvo DP drive as well. Thats about it. It ran 58mph with 25 gallons of fuel 2 adults and 2 kids. I've read faster alone once with a full tank (50g).
I think 68 is a little high for 22' 280 hp alone. It may do it but I would be surprised.
I will tell you this... my boat launches out of the water and I would suspect this 22footer would do the same.