OG should definitely be the centerpiece of your studies, but it's worth going through PR and Kaplan to understand test taking strategies.

Check out some of the resources here, https://www.beatthegmat.com/resources.html. There's a lot of info there to help you structure your prep during your limited time period.

Good luck!

Basically, the OG is enough if you are studying in the right way. If you are not studying in the right way, then it doesn't matter what you're using. Just doing the OG questions (even multiple times) is not necessarily enough unless you are also figuring out:
- multiple ways to approach the problem - both "official" ways and "test-taking technique" ways
- the best way for you (combining both efficiency and accuracy - remember, you only have 2 minutes per problem, on average!)
- how you will recognize what to do with a particular problem, and how you will recognize that a certain way is likely to be the best way for you
- how to make an educated guess
- what traps exist and how to avoid them
- what shortcuts exist and how to spot them
- what to do when you don't know what to do
- what mistakes you made, why you made them, and how to avoid making them again
- and so on

I can easily spend 20 minutes studying just one problem before I'm done extracting all of the lessons I can learn. If you can do the above effectively, then yes - the OG will be sufficient to get a 700!