In Rottweilers a 36" crate is sometimes referred to as a "bitch crate," and a lot of people use them at shows and in cars. I don't know if they also use them at home, but for me 36" seemed too small to be really comfortable, and I used a 42" for my females, who all weighed about 85 pounds.
Like dobebug I have a variety of crate sizes. Have never used a divider, and I'm probably wrong to find reasons to worry about such a thing, but I do. Gibbs the German Pinscher was close to Doberman size as a puppy -- 20 pounds when I got him at 11 weeks. He started in a 24", which was big enough for him and his Cuddle Puppy, and went through a 30 and 36. He's now in one of the 42s I had for the Rotties. He is oversized for a GP at 52-54 pounds, and if he stretches out he can use all that length, but he can also curl up and make it look ridiculously too big. That's fine with me as I want my adults to be able to stretch out comfortably in their crate. For that matter I don't squash puppies as tightly in a crate for housebreaking as I often see recommended.