GMAT Strategy

Hello all, I've scheduled my GMAT about a month ago for next Thursday the 21st. After going over the practice tests (one from Manhattan and one GMAT prep) I scored 590/600 on both. My struggle is that I really want to attend a t-10 school next fall (2012) and know the importance of getting a solid score on the exam. My undergrad GPA was a 3.9+ and I currently work as a FA at IBM with global scope. With that being said... I know I still will need a 700+ most likely to be considered for the universities I want to attend. Should I postpone my exam for another month or two and allow more time to study? I'm very willing to go that route however I also am a little unsure what the extra time will really help me with in terms of preparation. In the OG I answered 217/230 for the problem solving correct and within 1.5-2.5 minutes each so the fact I'm struggling with the math sections on the practice tests is really throwing me a curveball. Also, I seem to have some difficulty in terms of the reading comprehension and sentence correction but I accredit some of the poor scoring to laziness when taking the practice tests.

All tips and suggestions are greatly welcomed and appreciated. I'm putting a lot of pressure on myself to perform well on the exam... and if taking a course will help me break into the 700+ realm I'm open ears to that also. Thanks again!