Ah paddles again.....
Here's the (dubious) wisdom I've come slowly to after years of joining paddle discussions.
A paddle is a paddle is a paddle.... As with bicycles where a pound on the frame is as great as an ounce on a wheel . . . .It's not those stretchy pants that's made Lance Armstrong.
If one paddle hurts your shoulders and another doesn't -- great, but it's muscles not paddles that's at fault. Skip buying or carving a new paddle, start off with a little weight lifting. With a little more weight lifting you could duct tape bricks on a wing paddle and feel no pain.

I'd like to hear what a world class paddler says after he/she paddles with a range of GPs, Euros, wings, a 2x4. I'd like to see the GPS results.
I'd like to read a really good scientific discussion of paddles. Paul Davis's contribution is good. Apparently conceptual physics is not well practiced even by grad students in physics. I'm constantly embarrassed when I learn something new (like the net buoyant force on all of us from atmospheric pressure.)

I am greatly suspicious of the strange rituals around GP paddles. The short-loom-vigorous-sliding-hands business? I doubt any Inuit or Aleut would engage in this sort of shenanigans except while waiting for a longer pick of drift wood to wash up on shore. Every (old) movie I've seen (and watched repeatedly frame by frame--I love DVDs) of Inuit paddles shows them hammering away, no sliding, no canted blades...
We should also consider that it's mostly middle aged kabloonas, who do not live as hard as did the Inuit/Aleuts, discussing this subject. We are likely much larger and less tough than the short skinny giants on whose stronger shoulders we stand so tall. Those scrawny guys in the old photos are very likely as strong or stronger than anyone of us, or anyone we might meet. Consider a bunch of 5'10" 50 year old guys each weighing 200 or so pounds discussing what a bunch of 5'-0" 25 year old guys weighing 130 pounds have done. (For most Aleut paddlers to be like us, they'd have to throw a seal over their shoulder 15 years after they died).

I like GPs, I've got one, and a glued up blank for another (if I can find it). Haven't used 'em though since I snapped the first 4 years ago.
I've got two Werner Euros a Camino that's too long for me and my kayak--that used to cause me endless shoulder pain, and a shorter one--I can't remember the name. I use them high angle and hard. After full ACL repair to my right shoulder, physical therapy and weight lifting (Sea Kayaker Magazine a few years ago) I can hammer either paddle for 3 hours. The only soreness I notice is when my girlfriend later massages my shoulders. 'Oh, yeah, they were a bit sore, thanks sweet.'

90 percent plus (kayak) paddlers I see are slow moving, weak, bad stroke. The few I see who know what they're doing move quickly, and never much discuss paddles.
Weights, work on stroke form, skip the voodoo rituals.

Remember I said: dubious wisdom.