I attack my Sensei (When demonstrating a technique) pretty much the way anyone on the street would. Not because I want to prove a point, or that I want to test my Teacher, no.. just because, sometimes, you have to, It helps build more confidence, it refines your technique, and enhance the senses. Doing Aikido slow and secure all the time is great, but sometimes, speeding up things really give different results.
I also do surprise attacks on my Sensei (and other Aikidokas) in the middle of our practice, it's sooooo much fun!
Sounds like a good way to get hurt to me.
We often do waza quickly, fast, hard, etc.
I just don't think I need to either feel full power/full speed from a relatively young, still quite fiesty 7th dan. He can throw me quickly, or hard, but preferably not both at the same time, and not full on. Maybe someone under 47 without herniated discs in their neck would feel differently.
As to surprising people...I tend to dump people pretty hard who do tha to me. They rarely do it twice. Sometimes people end up going to the ER after stuff like that. I can understand doing that for a limited period of time (such as preparing for a dan test), but on an ongoing basis? I think that is just begging for an issue.