Hey SandS, have a look at the video DJ made of the Great Melbourne Paddle
www.seabreeze.com.au/forums/Stand-Up-Paddle/SUP/Starboard-Great-Melbourne-Paddle-vid/ and watch Annabel paddle, she really gets her legs, glutes, hips into each stroke. A lot of forward motion generated from bringing her hips forward as she prepares for the next catch. Jacko and Ang look similar, obviously I'm simplifying things too much here, would be great to hear from Jacko on this. Paddled quite a bit with her over the last couple of weeks and she has changed my stroke, she says that paddling is NOT an upper body sport and that you get the real power from your strongest biggest muscles, glutes and quads. Anyway I've started using shorter paddles and getting more body motion into my stroke (well trying!) and it takes a huge load off the shoulders. I've been having trouble with one shoulder and it's partially because I was just powering everything from upstairs, started using my surf paddle which is 7" overhead for everything and going to go shorter for surf.
Don't get too caught up with changing paddles to fix things like sore shoulders, I'm convinced at lot of it is to do with technique. Of course light is good, you are just wasting energy with heavy paddles, super light paddles are like night and day to 'regular' paddles, spend a little more and look after your body IMO. I'm really noticing the difference my very light KenNalu makes to fatigue over longer distance. (pimp alert, I'm importing them!!)