At my dojo, speed has nothing to do with the success of a technique. In fact, attempting the technique as slowly as possible is a great way to learn the proper mechanics/feel. If you can do it slowly effectivly, then you can do it fast when necessary.
The uke's role is to maintain the static as best as they can, however once they feel the move working, they are to relax and continue the connection to the end of the move.
If you are performing the technique with that particular uke check a couple of things.
1. Sometimes uke's efforts to maintain nice tension get overzealous and they prepare tension that "follows" the move (i.e. they know where it is going so they anticipate).
If this is the case, you should feel that separate technique would be called for (i.e. they may be blocking shiho, but kotagaishi is eaiser than usual.) In this case the uke is not practicing correctly.
2.Your's uke was right and you are just muscleing through your moves. In this case, try absorbing the attack a little bit more. This will bring uke off balance and make your technique as easy as pie. It is kind of like cheating, but drawing the attack off his/her comfortability zone is one of the most powerful devices in Aikido.