7 on my own....but one day I managed 9 with a girl, and the rule was she was only allowed to give me handjobs. She had great big tits though which looked great when she was wanking me.
I have to say once I get to 4 or 5 the cum is non-existant but the orgasm is more intense, it usually moves through my whole body. I do have to really work it hard though - up around 7 is a very hard and fast wank over some real hot video!!