damn it, gonna have to side with skiierman on this one..
Things you DON'T want to do with an ugly girl: go down on her, put your dick in anything BUT her mouth. Nothing wrong with getting head from a less than fully attractive girl. Sure, she's not hot but better than nothing. At least you won't feel the need to throw up, won't have any ugly kids running around or having to admit to other people about it..
Problem is, a lot of girls like to give head so as foreplay for you will fuck them. Then the complications arise if this 6.5 is really that hideous... OP just doesn't want to admit she's really like a 3