Hi
RiyaJain69The GMAT is meant to make a test-taker think during the exam. Before my first attempt, I too thought that familiarity with math problems will be crucial. But the final exam had questions I had not seen elsewhere. So don't bank on the familiarity of problems, bank on the familiarity of concepts. By the latter, I mean your foundations should be solid, and you should take notes while solving problems that hit you by surprise (in practice). So if at all you spot 'similar' problems, you can apply those concepts.
Coming to OG- since the OG is by GMAC, it is the most ultimate source of truth. So, questions can be expected to be of a similar vein in the GMAT. Then there are sources like
MGMAT on which you'll find good questions on par with OG questions. The challenge isn't familiarity, it is thinking methodology.
Speed comes with practice. Focus on accuracy first, and then speed. And if what I've written makes sense, leave a kudos!
Saurav