Have you experimented any further with sankyo since your initial post. This thread was really interesting, and I always enjoy getting different perspectives on the basic techniques.
I actually visited another dojo (a few, in fact) and nobody could seem to actually apply sankyo effectively on me. People either didn't get a lock at all, or the lock was concentrated on just the fingers and/or wrist.
I actually prefer to bypass the wrist completely and manipulate the bones in the forearm and upper arm instead.
And, when it came time for the actual take down, people tend to throw the lock/uke away from their own center and try to make a large arc in the air (like going fishing). While this may work on a compliant uke, all it does is cause nage to lose control over uke and puts uke back on his feet and grounds him even further.
What I do is keep uke rotating in sankyo and then drop his arm straight down to the ground and let his arm straighten out naturally right through my own center, where the not in your belt would be. But, because you are taking up that space, you rotate quickly about your own center-line and allow uke's arm to pass through the space you were just in. Uke will drop straight down to the ground over the same point his arm was pointing to the entire technique.
if Uke doesn't go down right away from this drop, you wind up in reverse Ikyo. If this happens, I carve on the spot just behind the elbow with the sharp edge of the bone in my forearm while lifting slightly on uke's wrist (like a see-saw). I don't push on the arm. I carve straight through it by sinking my elbow and punching either the ground below uke or at a line which goes through uke's arm to his chin. I don't bother bringing uke in a downward spiral and tenkan around. To me, it's a waste of energy and less ineffecient than just putting uke straight down.
I must say that this version is a much more painful and violent than the "nice" way most aikidoka do it. But, it doesn't rely on pain compliance, it works because uke has no choice in the matter. I doubt it is taught in most aikido dojo because it may not...fit with the philosphy of blending and such with uke.
I know it's hard to picture. But uke's wrist and arm stay over the same point on the ground the entire time. The lock/throw is centripital rather than centrifugal. And uke goes straight down to the triangulation point between his legs.
When I showed a nidan this at another dojo, they were very surprised.