Hi Aaln1,
Well, we'll have to see about the new relationship, but there's definitely something in the air! I'm currently away for two weeks, though, and can't really proceed with the courtship. And who knows, maybe she'll seduce someone else while I'm gone, you know how them French ladies can be
Anyways, talking about sails and performance, my personal experience is, that new rags can really have a big impact on the boat's abilities. I had a sail plan similar to 4800 in my old boat, with a big genoa and smaller main (the boat was a lot smaller, though). I used to do some club races and even participated in regional rankings, but had difficulties pointing as high as comparable boats. The boat also seemed to heel more than most. I then changed the oldish but ok dacron genoa with a mylar coveted one, and updated also the dacron main with a new one, better cut and with a free foot etc. The impact was drastic. I gained almost half a knot pretty much throughout the speed range, and even more in light winds. I was also able to point several degrees higher, and the boat was not heeling as much as before either. And as a concrete proof, I also started to score some points, being able to sail close to my handicap much more easily. In your case the effects wouldn't probably be so profound - if any - since you already have decent sails, but nevertheless, it probably wouldn't hurt either. But as you say, that's a very expensive way to try and improve the performance, especially in a boat the size of 4800.
Also the rig configuration might come to play. I don't know if all Dufour 4800's have checkstays, but at least the one I'm looking at has them. I've no experience of checkstays personally (yet), but I've heard, that they can have a considerable impact on how the boat performs upwind. In my understanding the checkstays able you to keep the mast from bending, when you increase tension in your backstay, thus having more tension also in your forestay. If that's the case, then at least my old boat would have benefitted from backstays, because I had real difficulties keeping the forestay from flexing too much, when pointing in medium winds. Do you have checkstays in your boat, and if so, have you noticed any benefits?
That's an interesting point about the design of the 4800 hull. It might well be that the era in which she was designed, is a factor in her ability to point. However, I would still expect her to be able to point at least as high as the modernish pure cruisers, say 32-34 foot Bavarias and Jeanneau Sun Odysseys from nineties and early 2000's. Do you think she can match them? In any case the overall performance of Dufour 4800 seems indeed not to be half bad, at least judging from her handicap. For example the German Kreutzer-Abteilung yardstick seems to give her a general handicap of 102, which translates to a decently quick ship, only a bit behind the older Dehler 106/34.
Finally, you asked where I read about people emphasising the importance of good sails to 4800's performance. I've been to a myriad of websites trying to find info about Dufour, but I'm pretty sure it was on the francophone site called hisse-et-oh where somebody mentioned it. I tried to find the exact thread but failed, though. I think another mention was by someone doing some globe trotting with a 4800, but I failed to relocate that site, too. Sorry I couldn't be more exact, but I'll post it here, if I bump into that info again.