This is my personal experience on the matter.
I was at a seminar with approx 100 people in attendance. There were aikidokas at various levels and they came from all over the country. One of the yudansha (Nidan) in attendance was a real bruiser (Lets call him Biff the Bruiser). He must of weight at least 230 lbs.
During the seminar we got into groups (about 8 people) to practice a particular waza. When it was Biff's turn up he slammed this 100 lb. female aikidoka into the mat.
You could see that the woman was quite dazed from the throw, but she got up slowly and walked it off (A real trooper). Not only does Biff out weigh this woman by over a 100 lbs., but she was only a beginner (Gokyu). I'm all for yudanshas and high-ranking aikidoka going hard on each other, but this was not case.
I guess the other yudanshas in the group agreed with me. They each in turn proceeded to drive Biff into the mat with all the power and speed they could deliver.
It was an impressive if not brutal display. We must have performed three or four rounds of the technique and every time it was Biff's turn to take ukemi he was drilled and pounded into the mat. Sometimes I didn't think Biff would get up, but I guess his ego got the best of him.
Afterward you could see he was very shaken, and throughout the rest of the seminar he was a lot less gung-ho when performing a technique.
To be perfectly honest, if I was a yudansha at the time, I would've been up there drilling Biff into the mat with the rest of them. Some lessons are best taught by ones peers.