I was wondering the same thing as I've got some angels who'll need to be downsized in my 65 and I wanted to put some in my discus tank also. Be interesting to see the replies here.
Wouldn't it come down to the individual character of the angel? As in some may be timid or may be aggressive. You don't want to put a passive fish with a aggressive fish?
I know Marie had tried putting her angel back in with the discus and the angel was ramming the discus so out she came again. She was bigger than the discus though (I think that's what happened ~ Marie, correct me if I'm wrong?)