My 2 cents kind of goes against everyone else. If you are confident you can score in the 160s for the September lsat, then I would take it. Nothing can really prepare you for the conditions of test day, so getting your nerves knocked out before the Dec lsat may improve your score even more on top of your extra studying time. Let's say you get a 160 in September & then a 173 in December... the admissions committee isn't going to write you off because of a 160 on your first try. 4 attempts on the lsat would probably hurt your chances, but 2 tries? Highly, highly doubtful. Worse case scenario, they ask you about it during interviews. Good luck!