At a cinema, six. At home, seven I think. Cinema has traditionally been tiring because it tends to be all nighters. Last I did was five Dario Argento films, preceded by Mandy at a different place. Wad flagging during Deep Red, had to rely on the score to keep following it. That was the fourth film of the night, between 4 and 6AM. Without regular tiredness and with decent but not over taxing films I can do five happily, six at a push. Seven is mostly just for when I'm being a bid lump, or have some perverse sense of a mission.