Question is broad. Where do you have the most trouble? RC? CR? SC?

In general, I think SC can be improved with the greatest effect in the least time, so I would say to study that. With only a few days left, there's no need to get into a book. Flashcards offer a great way to solidify the concepts you've learned by offering a high volume of feedback in a short period.

I would recommend the Flashcards from GMATFix because they are interactive, and each card has exercises, a lesson and often further examples. Go through the free sample GMATFix Verbal flashcards (https://www.gmatfix.com/flashcards_verbal.shtml) to determine whether you can benefits from their format.

If those don't appeal to you, you can try the ManhattanGMAT flashcards (someone please provide the exact link: www.manhattangmat.com). Manhattan GMAT generally makes very good materials so I think their flashcards will also be good.

Hope this helps

Actually, SC is my best question type. I do very well on RC and CR till I start hitting the 700-800 level questions, and that's when I start to level off in the section overall.

Is there a quick fix via flashcards for these question types, or should I just focus on SC as you said and aim for complete mastery in that area?

There's definitely no "quick fix" for RC and CR - those are the two most subtle question types, and don't really lend themselves to memorization. Really, the best advice is simply to do lots of upper bin RC and CR problems to get used to the patterns and wording that the test writers use so that you'll have better "hunches" on test day.

It probably isn't a bad idea to keep working on SC as well, to aim for 100% in that area. SC does lend itself to memorization; if you haven't learned the main error types from a prep book yet, you can definitely still improve in SC. I thought I was pretty good until I had my eyes opened by some of the common strategies!

When I was taking my first few practice tests, I was scoring around 38-39 in verbal on a regular basis. I was also finishing with 7-8 minutes remaining. I quickly realized I could take more time in verbal (I am a fast reader). After taking more time and analyzing the difficult questions at greater length, my scores increased to the 42-44 range. If you don't have lots of extra time now, maybe you could speed up your SC since that is your strength. Hope this helps.

That's a good point - I was the same way before I really put in serious verbal study time. I would finish 15-20 minutes early, with great but not spectacular scores. Once I slowed down, my score went up into the 99th percentile. Make sure you're using all the available time - there's no point leaving time on the table, no matter how badly you want the GMAT to end.