Well, any snake no matter how calm or laid back can have a bad day. They are still wired by nature and dont really get domesticated like a dog. So with that said, my 7' female BCI, Rosey, who i have had for 6 years or so since she was a little 18" worm, did tag me when i startled her. She has never bitten anyone even when the vet stuck a needle in her nose to get a culture. The most she has done is hiss once or maybe twice. So anything is possible.
I do agree though, a mellow larger snake is more pleasurable to deal with but for anything over 13 feet, i would want a spotter just in case.
And retics are great but they require a lot more than boas. And generally they are always on the go. With my boas, they are content to just stretch out on me and usually hang their head down looking at the floor.