It's illegal -

Sec. 15-140m. Reckless operation of a vessel in the second degree.
(a) A person commits the offense of reckless operation of a vessel in the second degree when he (1) operates a vessel at such speed or maneuvers a vessel in such a manner as to endanger the life, limb or property of another person, (2) operates or, as owner, permits the operation of a vessel loaded with passengers or cargo beyond its safe carrying capacity, having regard for weather and other operating conditions, (3) operates or, as owner, permits the operation of a vessel loaded or powered in excess of the maximum capacity information stated on the United States Coast Guard capacity information label or the capacity information label of the manufacturer affixed to such vessel, or (4) operates or, as owner, permits the operation of a vessel the capacity information label of which has been altered, defaced or removed. (b) Any person guilty of reckless operation of a vessel in the second degree shall be fined not less than fifty dollars nor more than two hundred dollars. (P.A. 89-388, S. 13, 27.)

If it's a vessel that never had a capacity label then they would not be in violation as there is no horsepower label listed for the vessel. It would fall back on unsafe speed, movement, etc. if something happens. from above - (1) operates a vessel at such speed or maneuvers a vessel in such a manner as to endanger the life, limb or property of another person

I know some of the old wooden Chris Crafts from the 30's through the 50's had some monster V8's in them. I'm sure in today's equivalent boat they couldn't get away with the larger engine.

Thank you, its nice to finally get a straight answer. I can't stand anecdotes and "I think so, therefore it must be, but I can't support it, so you'll have to trust me."

My searches were all using terms such as "motor", "engine" & "overpowered" which was used in the handout... should have been looking for "capacity".

The part (b) of that proves my point about inept bureaucrats not reviewing their published materials - a fine of $50 - $200 is a lot different than "may instruct the operator to return to the nearest mooring"

What I posted is Connecticut's regulation. Each state can have something different however I believe they are all trying to mirror each other on boating safety laws for the most part.

I agree but it doesn't appear to be federally enforced, so in theory you'd be all set out in federal waters but you'd have to moor the boat and swim a long way in depending on where you crawl out.