Everything is 1988. Engine is in mint shape, I've had a compression
check and inspection done. (I know how to do it myself but when I
bought it I talked to the mechanic who checked it over)

The hull length is actually 26'5" but with pulpit it's 28'2".

Beam is 8'3" and weight is 5900lbs.

I'll play around with it soon and check the numbers. I know when I
went out with the previous owner during the sea-trial we'd kick the
RPM's down because they did seem to jump but I don't remember how high
they went.

WOT range is supposed to be 4400-4800 but I believe it was running
higher.

So let's go with a 26' cruiser. What is a "general" cruising and top
speed for a 26 foot hull length cabin cruiser with single engine? I
know hull design and beam make a big difference, but I'm looking for
some ball park numbers.

With the 14.5x17 according to his logs, gas mileage ranged from
1.5-1.9 depending on passengers and weather conditions. In 4-5' waves
it did not stay on plan and dropped to 1.1MPG.

I've been using online calculators but they all show a pitch of 10!!
I even plugged in other boat/engine configuration, it also recommended
a pitch of 10 for a Sea Ray Sundancer 260 so I'm not sold on it being
accurate.