I agree with HYSHopeful on all of this.
I think you'll find that at some point, LGs will just 'click,' and you'll start getting 0-2 wrong per games section. Beyond occasional review so you don't forget what you've learned, you won't need to study them anymore. Games are the easiest section to learn, so start there - LG drilling will provide the most immediate results.
That said...LG are only 1/4 of the test, so that's not enough to get a 170. As HYSHopeful noted, you probably aren't going to score a 170 with a -12. On the legendarily brutal June 2007 scale, -12 was a 166. In addition, most people go down a few points from their practice scores on the real exam. (Everybody assumes they won't be one of those people...and then they are.) So you're probably going to want to kick it up a notch.
But you have three months; you can do it. Focus on LR (in addition to LR counting for more of the test, RC is harder to improve.) Learn, live, and love the Bibles. Pull the questions apart. Don't just plow through Preptests - really analyze the questions and why each answer choice is right or wrong.
Finally, make sure you get your hands on *recent* (2005-on) tests. This is crucial, IMHO, because the test has evolved over time. Games have gotten easier, RC has gotten harder, and LR has shifted in focus. And in general, the scale has gotten tougher; I don't think there has been a -12=170 scale since 2004. Save the recent exams for the last month before the test, when you've built up your skills. These tests will give you a more realistic estimate of how you'll do on test day.
Additional Comments For LG:
I'd recommend working through about 40 to 80 games at your leisure (from preptests 1 - 20). (Don't worry too much about spacial games and other oddities that haven't shown up in years.)
After you've done that, then I'd go through the LGB again and really absorb the material therein. The LGB will take on a new meaning after you have struggled through dozens of games on your own.
On PT 20-40, try and get down to -3 or so per section under timed conditions. Remember, anyone could get 24/24 on a games section if they had 15 minutes to complete each game. Work on pacing and use PT's 20-40 to develop your sense of timing and to try and get down to -3, -4 per section.
PT 40-53 should definitely be taken in the two weeks preceding your test date (if possible), and each exam should be taken as a whole. By 45 or so, you should really be scoring in the -2 to -0 range every time, hopefully with more -0's than -2's, and [ideally] finishing with 25 to 90 seconds to spare.
That is the basic progression that I went through with LG, and in June 2008 I finished LG with about 2 minutes to spare, feeling fairly confident of my performance.
Laura is right, the test has evolved over time... This is why I'd recommend taking the exams in chronological order. This way, you will have taken the most recent exams immediately preceding your actual exam. This will ensure that your most relevant prep work is done in the days prior to your taking the exam.
I think that the actual test material has gotten easier over time, but the scale has gotten correspondingly unforgiving as a result.