Hi a03,
To start, choosing to study for the GMAT now - far in advance of when you'll actually "need" your GMAT Score - is a smart choice. A Score Goal of 600+ is relatively modest, but the average Score on the Official GMAT hovers around 550 most years - so you're interested in an above-average result. As such, no combination of GMAT study resources can 'guarantee' you what you are looking for. You will have to learn and practice a great deal; thankfully, the GMAT is a consistent, predictable Exam, so you CAN train for it.
Since it sounds like you're just beginning your studies, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can take 2 for free at
www.mba.com (and they come with some additional practice materials). If you want to do a little studying first, so that you can familiarize yourself with the basic content and question types, then that's okay - but you shouldn't wait too long to take that initial CAT. That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 3.5 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can come up with a study plan.
I'd like to know a bit more about your timeline and goals:
1) From what you describe, it's not clear how much study time you plan to put in until June. While you are still in School, how many hours do you think you can consistently study for the GMAT each week? Once we get to June, how many hours will you be planning to study per week?
GMAT assassins aren't born, they're made,
Rich