I owned one of each (Hull 45 TPI built and Hull 406 French built). Aside from hull 45 losing her keel and sinking (long story - search the archives) it was a good boat when I owned it. The French boats have a superior build in most ways: molded in toerails, foot braces and winch islands, shorter stanchions and pulpits, properly framed windows that don't leak, and clear coat anodized spars instead of painted. Performance-wise they did not seem to be any faster but I have been out of the class for a long time so things may have changed.
I think the J-80 is a great boat that does many things well and would have been awesome with carbon spars to enhance performance and simplify trailering.