Definitely depends on the roo. When I put all the roos but one meek one in Chicken Jail, the girls fought amongst themselves almost constantly, always jockeying for position. When I put just one very dominant, manly roo in there, he laid down the law and everything settled down. So now I have two roos per 10 hens, but since the one roo is so meek the girls are OK. The meek roo, Mordred, only mates his favorite girls, and not often (not all my Buttercup eggs are fertilized), while Hugo is less picky and will mate EE or cochin hens, but does it reliably.
Edited to add: As of now I have two roos in the Bachelor Pen. The weirdest thing happened a few weeks ago--one hen, which I was sure had become coyote chow months ago, somehow flew back into the barn with the chilly nights, and started roosting in the rafters by the Bachelor Pen. She wouldn't let me catch her, but when DH opened the Bachelor Pen gate, she went right in. She has since settled in and the boys cuddle up to her and protect her. She isn't missing any back feathers, she doesn't appear to be over-mated and in fact I've never seen her get mated at all. She hasn't laid any eggs for me either, unless of course she's hiding them really, really well. Think I'll get peeps this spring?