Keith you point about speed is really well taken. Speed and momentum obscures flawed technique and those flaws invite injury. What I find myself doing these days is taking uke's attack at whatever speed it comes in at and then buy the time the throwing kazushi occurs I have slowed down and often find myself shedding momentum from my hara only half way through the movement and letting the arms die. The throw occurs at reasonable speed but I get to do the initial parts just as fast as uke enters. I don't know if I would have trusted myself to do this 5 years ago.
I'll have the students try to do it at as slow a speed as possible with uke trying to feel if there is any opening anywhere. And by that I mean a loss of lead, kuzushi, connection or slack coming in to play. Then, and only then, start going a little faster. Or have them adjust the speed constantly to just mess with uke. So they can feel what's really possible and that the point isn't the speed and power, but the connection and smoothness.
Or is it just that silly aiki thing again? Hmmm. :P