Several years ago I tried a GP and now the only time I use a Euro style paddle is in the creeks. I have had some long days with with my GP ( 40+ miles ) and loved the fact that they do not work you as hard as a Euro paddle. Bad weather has not been a problem as I have been able to keep a constant and steady pace for a longer period of time with the GP.
There is a some good Info at http://www.qajaqusa.org
on GP paddles.