I can do about 5 or 6 one handers. I can do about 35 regular pull-ups. I can do 1 or 2 pull-ups with 100 lbs hanging.
I think when you can add like 50 lbs to one pull-up, one handers will start to get easy. Also, when you hit point where you're doing sets of 25, the grip (pull-up, chin-up, close-grip) stops mattering.
Also, maybe It's just me, but doing true one handers, with one hand at your side is not THAT much harder than the ones where you grip your wrist, but I always feel like I'm going to hurt myself. So watch out.