I'd never sailed under just a headsail until last Saturday, when we raised the main on a friend's fractional Jeanneau 36i we noticed a chunk of the halyard missing. Wind was 20 to 25 kts. and we just didn't trust it to hold ( guests aboard), rather than bag the day we went out under just the genny, maybe a 135-140 laminate (new). To our surprise the boat handled just fine even in a rather horrible sea state with large waves with no space between them, just breaking wave, trough, straight up and down wave, rinse and repeat. No discernible weather helm, even when gusting and going to 30 degrees heel, pointed as good as we dared etc. We were still making 6.5 knots or better, it did make us think we aren't getting near enough out of the rather flat cut main (old, rather heavy for our area), so we're working on that.
I think I'd still prefer just a reefed main on my Catalina, the 2 boats have a much different helm feel.