I don't think the 4-5 thing is a true rule at all. And if you spend more time studying, you'll definitely become better and more consistent. It's more of a question of whether you want to wait another year than anything.
well...i dont know how to give u advice but to give you my own situation. i was testing 169-171 (very tight range, i know) before the sept 2006 LSAT. i got a 166. decided to retake after much consideration. hardly studied. maybe did 3-4 prep tests again before the test and reviewed powerscore bibles. got 173. i dont think i'm an anomaly or anything...so if you felt unusually stressed during the LSAT or feel you ddint perform as well as you could have...then maybe you should. if you test your preptest range in the mid 160's you have a pretty good shot at USC.