First paddle today with a new Novorca GP (Model 88A, 88 inches, 20 inch loom, 3.5 inch blade). Started in calm Mission Bay, San Diego, exited the slightly bumpy with wakes and incoming waves channel entrance, went north a few slightly choppy open ocean miles, and returned.
The carbon foam core paddle is elegantly beautiful and very light. I had owned two previous GP’s which I never took to; a Superior whose square shaft gave me blisters, and a Beale paddle which seemed too heavy. Personal taste, perhaps, but if you can afford it there seems no comparison between carbon and wood.
For many years I have used low angle, bent shaft, paddles: A 226 cm AT, and a 220 Werner Kalliste, which I like equally and use interchangeably. I basically used the same fairly low stroke with the GP as I do with these two. The most notable immediate difference was at the catch, where both Euro’s immediately grab the water, while force builds up more gradually with the GP. Another difference was that the GP tip went much deeper than either Euro does. (Is this good?)
For the first 20 min or so there was a bit of flutter. But I played around with a bit of cant angle, as I have read about, and it was easy to settle into no flutter for the next two hours. The cant is very subtle seems to come about naturally.
My time out, at moderate effort, was 71 minutes for about a 4 NM course as opposed to my usual 62-65 minutes. So I was definitely slower than usual with my Euro’s. (This was a bit of a disappointment.) I did not notice any less fatigue. Perhaps the many efficiency comparisons between GP’s and Euros have been with high angle Euro’s or wings, not low angle paddles. As of now, my feeling is that the low angle Euro is at least the equal of the GP for efficiency.
I found it difficult to get a consistently clean catch, especially in bumpy water, and the paddle noise when I did not clearly provided feedback about that fact. I would get that noise every 4 or 5 strokes if I did not pay attention to sitting upright/forward and “spearing the salmon”. Otherwise the paddle was totally silent with no ventilation.
The grip on the shoulders was ok, but the ergonomics of the bent shaft just seems nicer to me.
Bracing was different. Without shifting hands the quick high or low brace of the Euro paddle provides quicker support because the blade is out farther. OTOH shifting the whole paddle left and right was very nice indeed. In any event, I felt confident transiting the bumpy water. I did not try any rolls today.
The GP has a simple elegance that is very pleasant and I enjoyed the day’s journey, despite getting used to something different. It seemed more rather than less fatiguing than my normal blades. I chose to get a GP whose dimensions are equal to those of Greg Stamer, who is my size, rather than the shorter and narrower blade favored by Duane Strosaker, who is also my size. The extra length and width gives better bracing at the expense of too much power.
(I am also going to post this on the Greenland forum. Hope I am not breaking any rules by doing so.)
Reactions
Just random reactions to parts of your post based on my experience and web postings. To start with, wing paddles and ordinary Euro paddles both require maximum expenditure of effort at the start of the forward stroke. A GP paddle delays maximum effort toward the end of the stroke. This is just what the paddles require. There is no good or bad about it. Second, the high angle/low angle dimension needs to be separated from the other dimensions. For the GP, the technique that Stamer descibes, which I use, is a high angle technique. The technique that Van Doren teaches is a low angle technique that many use but is completely different from the high angle technique. Third, low angle paddling with an ordinary Euro paddle can be a temporary thing to rest muscles or a standard practice. I think a case can be made for temporary thing. But that may be idiosyncratic. Fourth, I use Superior GPs and never get blisters. But I am careful to relax my upper hand and never grip the paddle shaft too tightly. Don’t know if that is what you do but I suspect your grip is too tight. Good luck in sorting this all out. 
my findings are different
when you say:
"So I was definitely slower than usual with my Euro’s. (This was a bit of a disappointment.) I did not notice any less fatigue. "
I find that using GPs gives me the same speed as Euro but on longer paddles (20+ miles) I am definitely less fatigued.
It took me a while to get proficient though and achieve a clean efficient stroke.
Still have a load stroke.
I’ve had my Lumpy paddle since about august and I’m just starting to notice I can have a fast and almost completely silent stroke. i don’t know if this is more efficient but it is better for sneaking up on things. With a Euro blade the stroke is very load and splash and there is no way around it.
I can paddle just as fast with a GP but it took me about 20 miles of paddling with it to be just as fast as the euro paddle.