Do people still believe Choppers sail "half a metre bigger" than their size?
I've had a few goes of the L (4.7m) and XL (5.3m), and if anything I'd say they sail as if a touch smaller. I'm using the matching Naish RDM 370 mast, though the 60% carbon version instead of the recommended 90%. I can't imagine it adds half a metre - have you noticed any difference in performance between the two masts?

Yes - if you are talking about the 1st gen (I can't speak to the new versions). Lay them over a sail of the real size and you'll see. I layed the XL ("5.4") over a real 5.4 and it's pretty much the same size except missing the top panel. That's how you get a 5.4 that rigs on a 370. Obviously, if you measured the actual area, you'd get less than 5.4 but since most sails have a fair amount of twist, that top part is providing very little power but does reduce induced (tip) drag. But these aren't speed sails so induced drag is not a significant consideration.

I've only sailed them with 90% masts so can't answer the other question. Have had a quiver for about five years now that I use for foiling.

Thanks. Yep, 1st Generation. I think they arrived in 2012 and the next few years, then a gap? then Mk2 in 2021, now up to Mk 3.

I saw your question and thought hey, I can answer it in a sec... but somehow realize that although I'm a pretty ok windsurfer I'm getting dumber in terms of equipment, wind speeds, tides etc... I have a good feeling of these relative to me (what to rig and use) and my skill but so maybe these Naish sails simplification did this to my brain

I have 4 of them plus 2012 XL version and XL MK2.. Frankly I never noticed much difference between XL 2012 and XL Mk2... I run them on Severne 100% 370 and like running M and S on 310cm Nolimitz skinny (it rigs perfectly actually). I remember when I got 2012 XL, I was absolutely sure that it pulled very nicely, maybe like 5.6.. What I like about them is how sloppy you can set them and, yes, that they all can be set on one mast.. It's not a speed sail.. but can go pretty fast..

I also remember when I first tried one in Maui, maybe it was the L, I didn't like it. It wasn't pulling... But maybe it was simply bad wind day.. Still I was silly enough to get all 4 thinking I didn't care about speed but cared more about screwing around and jumping and it would allow me to have equal power for the smallest possible sail.

I think that as with Boxers which gradually went more standard, Coppers follow... MK3 I would not get as it likely already lost that max power for size appeal..