I'm a recreational player that can't clear from baseline to baseline with the desired height and speed. I've read a lot from badminton central about arm pronation and the general form of the stroke.
I would like to know what the correct wrist position should be during point of impact. From watching players like Lin Dan and Lee chong in slow motion, it appears that the wrist is at about 120 degrees at about of impact. However, watching thejym's video on pronation, his wrist seems to be less than 120 degrees, thus the contact is not at the highest point like Lin Dan.
When I'm learning I try not copy amazingly good players. In my opinion these players are so good they might be able to do things us ordinary folks might not be able to do. Especially male players. So I generally try to learn from female players.
With regards to wrist, I used to use a lot wrist - now I am convinced the less wrist the better, supination and pronation of the forearm is what gives the real power - along with proper body rotation. Again, I consider myself an intermediate player - who seems to have been playing with the wrong techniques all my life - so I'm try to re-learn most of the strokes.
Good luck - I'm sure some of the more experienced players can give more feedback.