Re: does nikyo hurt?
I would say you should do it the way you are taught until you get very good at it and only then wonder about how others do it. That's discipline.
If you already are going to keep to that discipline before experimenting with other ways then there is no problem asking.
Ultimately I would say a really good nikkyo doesn't have pain as a part of it but that also is partly down to the uke being experienced.
Personally I can say I can do it with or without and in different ways. I would also say that the whole trick to nikkyo is maybe 10% to do with the physical mechanics and 90% to do with realizing it's a sword cut.