Well, here I am about to defend my decision to convert to a junk rig against two heavy hitters in the junk world! :)
Firstly, my decision to convert to a junk rig was "baked in" at the beginning of my build, but at that time I wanted to see how the boat handled as designed before going to the new sail. I had not sailed with a lugsail before and it seemed that there were many features similar to the junk sail, so I put off the decision until I had pretty much come to a conclusion after some experience. As it turns out I much preferred the sailing characteristics of the junk rig on my previous Hartley TS16. It was pretty much bullet proof in all weather and I never got into any trouble like I have on a couple of occasions with the lugsail. Yes the lugsail can be modified, but I still think it would not be a junk sail.
Secondly, I can significantly improve the sailing characteristics of my boat I am sure, particularly upwind, and in lighter airs. The first due to the better aerodynamics of a junk, the second because I can increase the sail area substantially simply due to the sail shape. The lug sails acceptably, but is both slow upwind, and doesn't point particularly well in any case. I cruise in the company of other sailboats, who are all bermudas, and I often lag behind on a long upwind run, which although I know that I won't achieve the close wind performance of a well tuned bermuda rig, this would improve with a cambered junk sail.
And on top of this, I am always up for a DIY project. I built the boat myself, and have managed several customisations on her already. This is one that I am very keen on doing.
As for the design of the sail itself, I was going to ask about the top panel issue. It seems to me that there are many junksails out there with a lower angled top panel, so I wasn't concerned about this. But there are other alternatives, such as reducing the sail to a 5 panel sail, which would keep the top panel and allow me to use my current mast. Actually the main reason for wanting to keep the current mast as is, is that I don't want too much overhang as the mast may exceed 6.5 metres, which is 1.5m longer than the boat. Not a major issue but it is a preference. If you think it is going to compromise the performance significantly I would keep the high angled top panel and either reduce the panels to 5 or extend the mast enough to accommodate it. Either way I am sure I can make it work.
And finally, I would still have a backup sail in the event that it is needed, which I don't have now.
Does all that make sense?