I just returned from traveling around China. Saw a lot of boats and a lot of funky homemade paddles, oars and sculling oars.

I use a Werner Shuna 210 or 215cm, but I also have an overlong Camano 230cm I think (slightly bigger blade), and I've used a Greenland I made;
I've also had shoulder surgery.

In short, I think my experience gives my two cents maybe an extra penny.
The Shuna length 210-215 is just right for me in my wide Great Auk, the Camano is too long, but I'm strong, aggressive and with the Camano I get an extra half knot from 3.8-3.9 to 4.3-4.4 over 10nM, but even with my rebuilt and strong shoulders....the overlong Camano begins to hurt. The leverage gained from the length I don't think is safe for my joints.

The Shuna, no problem-could go all day. The Greenland? Even before surgery when my shoulder was not working and hurt, the Greenland never hurt--that is a real benefit. It was a bit slower, we will never see a GP in the Olympics--but I also think orthopedic surgeons won't see GP users either.

Putting this all together. I think whatever sacrifice of speed with a Greenland is minor compared to the joint-safety gain. I'm OK with my Shuna, but I spend a lot of time thinking about and working on my stroke. If you don't, a GP is probably just right. I put the Camano back under the bungis--where it belongs-- as a backup, unless I get it shortened.

All those funky paddles, oars and sticks in China? I only got to try one, I could make a better one in less than ten minutes, but I think the Chinese boatmen are not worrying about an extra half knot. Shaft and blade length on oars and sculls seems important and given attention, but blade shape and paddles don't seem to get much attention at all. The hull shape seems more critical--unless you're tweaking for seconds and fractions of a knot. (which I do but shouldn't. I've got an ocean, 40 sea lions, a pod of dolphins and I want to get back in my car fifteen minutes quicker??? That's ah, screwy.) Guys on similar boats, in Shandong Stream, with a range of funky oars -- racing were almost exactly the same speed. Stroke cadence seemed the only factor. As much as we like to yammer about paddles the sticks didn't seem to be much of a factor.

Is this an endorsement of Greenland Paddles from a guy who doesn't use one? I'd like to think so.