Hi Muzz.
Those numbers are about right. Paddling with friends just youring I
plod along at 2.5 to 3 knots. When you light it up 4 + Knots would not
be out of line for a spring. Then there are things that twist that
curve all to hell.
Last year I met a croud of friends that had made a trip to Newfoundland
just to paddle. We went from Garden Cove to Woody Island in about 4
hours. We stopped and just poked all the way up there 13 KM + - .
I ate lunch at Island Rendezvous Resort and the wind had come up. The
bay was full of white caps.
It was 3:02 PM when I left.
I paddled back alone surfing all the way. I Stoped to talk to friends
aboard a ( the ) tour boat that was headed out for five minutes and
continued.
At 4:10 PM my boat was on the car and I was getting out of my wet suit.
About 13 KM per hour sustained over 13 KM all due to waves and wind. I
surfed most of the way.
I suspect I hit 16 or 17 KM + on some of those waves but I don't own a
JPS. There was a short crossing where the wind was not entirely in my
favuor.
That was in an NDK Explorer. Reasonably nice touring / expedition boat.

Re Hull speed and the likes. Don't wory about that: If you can keep up
with your friends that is all the speed you need.