Regarding your
reply to my post here I think there is no way to accurately break down percentages of who does what or how often.
Candaulism (or wife watching) could be viewed by many as similar to cuckoldry, but I think there are various acts and "attitudes/tone/temperament" attributed to one and not so much the other.
Candaulism is more of a voyeuristic activity (in my opinion) that could involve just "straight sex", meaning nothing kinky. Cuckolding may often be more within the BDSM realm, have a lot of fetish overture, be more female dominated in nature and have about a gazillion variations. So to answer your question, only the couple involved would really know but I suspect it would be more of the former than the latter. The only way to compile data like this would be to interview people, which opens up the possibly or even likelihood that some might embellish their story...or for others undersell it because perhaps the guy is humiliated to reveal that he was sucking on another mans balls when that guy ejaculated into his wife. :)
Candaules, King of Lydia, Shews his Wife by Stealth to Gyges, One of his Ministers, as She Goes to Bed by William Etty. This image illustrates Herodotus's version of the tale of Gyges.
Duke of Orléans showing his Lover (Mariette d'Enghien) by Eugène Delacroix.
This artwork is very well done, but in real life is just too damn busy for me.
I mean there is a lot going on there. :)