I go clubbing a lot and this is the mentality of my friends and I in a clubbing situation.
<7, may talk to just to be friendly.. but won't make a move. 7, Pretty good, probably talk to her to be friendly, if she's got a great personality, maybe make a move. 8, Cute, probably talk to her and make a move. 9, Hot, I'll most likely talk to her with the intention of hitting on her. 10, She's perfect, I can not leave until I've talked to her.
I've got high standards, but in reality, a 6 for one person might be a 10 for another. Generally I'd say 7+ is good.
7-8 range is like the range of "That girl's hot" but personally I only go after the 8+ but if you think you're hot chances are you are more of an 8 to most guys so ya 7-8 is usually hot it's just something like they could work out more is holding them back so ya like you said 7-8 is good looking.