I have a 89 23'5 Force and if I remember with the old stock motor(Magnum 365HP) it was around 60
These boats have a horrible design how hard it is to get to the front of the motor or waterpump with the back seat so close. If you want to know the easiest way to slide the back seat up shoot me a PM

I would guess 55-57 mph, mine with a full load is 68 and 72 with a light load powered by merc 500 hp. great boat, you will enjoy, really good in rough water if trimed right. the key to this boat is not to over trim.

have fun
scott