116-120: normal, hard to go wrong

110-122: usually fine, depending a bit on the dance and crowd

104-126: possible with the right dance and crowd, but on the edge of undanceable

<104, >126: almost never a good idea

Younger or more athletic crowds generally do better with another couple bpm, and vice versa.

This also varies some by community: some areas historically have had faster or slower music and those communities have many people who've adapted their dancing to the typical music.

As a musician, if I'm playing too fast or slow for the dancers I'm happy to be given real-time correction!  A caller watching the whole hall has a better sense of how well the tempo is going over than a group of musicians who are able to give the hall less of their attention.

Jeff