Hi Jonas,
Test Day is a rather specific 'event' - the details are specific and they matter, so you have to train as best as you can for all of them. The more realistic you can make your CATs, the more likely the score results are to be accurate. As such, when you take CATs in the future, you should make them 'match up' as much as you reasonably can with what you'll face on Test Day (meaning that you should take the FULL CAT, away from your home, at the same time of day as when you'll take the Official GMAT, etc.).
Since you have at least a couple of months of study time available, you could potentially raise a 610 to a 660+ studying however you like (for example, with just some general self-study). You've listed a Score Goal "range"; if you're interested in applying for Scholarships, then there will likely be a GMAT 'score requirement' as part of the application. This is meant to say that if you want to be as efficient as possible with this process (and potentially score a lot higher than 660), then you would likely benefit from investing in a GMAT Course of some type (either Guided Self-Study or instructor-led). Most GMAT Companies offer some type of free materials (practice problems, Trial Accounts, videos, etc.) that you can use to 'test out' a product before you buy it. We have a variety of those resources at our site (
www.empowergmat.com). I suggest that you take advantage of all of them then choose the one that best matches your personality, timeline and budget.
If you have any additional question, then you can feel free to contact me directly.
GMAT assassins aren't born, they're made,
Rich