If I had to take a guess from my own subjective observations at:
1) Their career choice
2) How they type on an internet forum
3) How they talk on workout videos
I'd say most of them should be below 100, but there are outliers, such as Milos, Sean, Chick, Nasser, Jay, Bob Paris, Mentzer and other past iron agers.
Milos, Chick and Sean seem intelligent, regardless of their character. Guy's like Ronnie seem stupid and Kevin Levrone sounds like a retard. I hear Nasser has a masters degree in history, so I'm assuming he's smart. Jay seems well spoken, so he must have average to above average intelligence.
Someone should conduct a study..
Maybe MattC, as he seems like the perfect guy to do it.