I would say Hog Islands or a Dumerils. Hogs get bigger than 5ft, the male I currently have out breeding females at a friends place is pushing 6ft right now and the female is around 7 or so.

Dumerils are very docile, and pretty calm compared to a lot of boas I've had. Biggest i've seen a male get is around 7 and a female 9. Maybe my friends just have freakishly large boas

I have both, and personally love each of them. I would have to say a dumerils for a first time boa though.