Dennis,
You may be right on the blunt LE. I used the same airfoil in my current PA plane that is very conventional (5 to 1 AR at about 625 square inches). It seems fine with turbulence, but the combination of a blunt LE with a fairly far forward high point and higher AR may contribute to the issue. I suspect that if I cut down the thickness of the wing and sharpened the LE a bit more I could go with somewhat larger flaps and possible mitigate the turbulence issues a bit. I still think that a high aspect, elliptical arrangement would offer the best of both worlds and will probably try that when next I dive into high AR designs. I have something on the board I've been dinking around with for awhile that is along those lines.
I agree on measuring moments from MAC to MAC and ignoring hingeline stuff. Ultimate, that's all that matters. I ended up using pretty big TVCs mostly out of self defense. I too figured that with such a long tail I wouldn't need a very big TVC to get the same effect I got with shorter moments and larger tails. But earlier planes with much smaller tails but long tail moments tended to be pretty unstable in corners and were kinda hard to control. As I went up in TVC the problems went away. And, of course, I really liked the authority a big tail gave when it came time to stop a turn. That's just impressive as heck when you're flying the plane. Let's see, I'll stop the turn right there and BANG it stops.
On the sensitivity to speed changes: When I started getting more reasonable on the AR, this became less of an issue, but I still think the more "one-speed" you can make the run, the better this sort of design reacts. You should have seen a couple of test beds I built soon after I built the Orange Crate. Someplace I have a picture (if I could find it) of an early high AR design I built. 9.8 to 1 with full span flaps (an I-Beam - Wow, can't believe I did that) with about 23% flap area. It was enormously sensitive to speed changes in turns. And way, way, way too light (650 square inches and about 45 ounces with an OS45FSR). I'm sure I was getting some flex in the wing, too. That probably contributed to it. I'll have to see if I can dig up pictures of that plane and an earlier one. Bot just looked so incredibly cool, but had real issues. The original high AR plane I built, first in the series, was called Dragonslayer and had some interesting features. it was heavily influences by the Orange Crate, but had a trike gear and an anhedral stab. That was interesting. I really liked that plane. Probably should have built another one (circa 1982).
Anyway, I think the combination of too high an AR along with too much flap probably caused most of the speed sensitivity. Since going to slightly less AR (in the 7.4 to 7.8 range) and cutting the flaps way down along with more consistent power delivery, the problems went mostly away while keeping the great turn and turn stability.
As far as payload and wing loading issues. I've always believed that every competitive plane has an ideal design weight. Certainly Paul has confirmed that with a standard Impact, the ideal weight is around 62 oz. As you go either way, lighter or heavier, the performance degrades. I think that generally, high AR planes seem to fly better when the wing loading is slightly higher than what you'd normally figure for to the wing area. You can't go crazy, but if a run of the mill Trivial Pursuit (645 square inches) performs best at 62 to 66 oz (this from Ted) and can still be competitive at up to 70oz, my layout at about the same wing area probably has a window of 65-70oz as the ideal weight for the lift potential. Figuring wing loading is all well and good, but I think more critical is the payload vs lift potential of the wing. There is clearly (at least from my experiments) an ideal you have to hit rather than just trying to make the plane as light as possible. But that just the way I look at it.
That's one of the problems with this. It seems that unlike conventional design, there are a lot more factors involved. Or perhaps it's just that more conventional designs have had more people working on them and so the various factors are more clearly understood. But it seems that while the general idea of these high AR designs is very good, there's just more to overcome. An Impact doesn't really have any "bad" habits. It does pretty much everything reasonably well (I'm just picking on the Impact because I've built a few and know the design pretty well). I really doesn't have any substantial deficits. It also isn't particularly outstanding in any particular area. It just does everything pretty well. In the hands of an expert pilot, it can be very, very successful (as Paul has illustrated). My high AR designs have some areas that they do pretty well also, but they have some areas that they are horrible and some that they are outstanding. Most of my goals with these things has been to keep the stuff that they doing extremely well and try to mitigate the things that drive you nuts. You probably can't entirely get rid of the bad stuff without also losing the good stuff. I just want to make the drawbacks livable.
This last design (last picture) pretty much did that. While it was still somewhat sensitive to turbulence, it was controllable and not too bad (it was a sheer joy to fly in an open field with no turbulence creating obstructions---even in pretty high winds). It had a corner second to none and was fun to fly. The tracking was superior to just about any other plane I'd ever flown. But did have a tendency, every once in awhile, to get a little weird if the engine wasn't right on or I selected the wrong prop or whatever. Consistent torque was a must.
OK, I rambled on on this subject ad nausium. I haven't built one in 2 or 3 years because I wanted to have some planes in the stable that were dependable and consistent. I've just about got that now and may go back to experimenting again. Stay tuned.