You know...that "the reviews seem to be heavy on improvements up to the low 700s but not as much on improvements to the mid 700s" piece is just about begging to be part of a Critical Reasoning problem! There are a few likely reasons for that:
-A lot more people score in the low 700s than in the mid 700s (based on current percentiles, 3% of all test takers score 740 or better, whereas 7% score between 700-730)
-Similarly, there are a lot more people starting in the 600s trying to get above 700 than there are in the low 700s (again that 3% of all test-takers) trying to boost even higher, so there are fewer opportunities out there to even have those kinds of reviews pop up
-Of the group in the low 700s trying to get to the high 700s you'll probably find a lot more self-study vs. guided-study than in the lower starting points, since at that point people are usually pretty confident in their ability and their mastery of the material but are fine-tuning pacing, minimizing errors, etc.
So there's pretty good reason that those kinds of reviews will be a little light. Plus, shoot, a lot of test prep is geared toward the average-to-above-average target group since that's where the market is.
Moving past the "explain the paradox" CR bit - in your case with a need to emphasize verbal pretty heavily, you'll almost certainly need to prioritize
strategy over content. I'd say a great example of this is in the GMAT Prep Question Pack (available from
https://www.mba.com), especially with Sentence Correction. When you go through the questions labeled "medium" you can usually pinpoint some common errors (pronouns, verb tenses, misplaced modifiers) as relatively clean decision points, but when you get to the problems labeled "hard" you almost always have to take a step back and really think about the meaning that the sentence is trying to convey and what functions the different portions of the sentence serve to that meaning. It becomes really heavily rooted in logical meaning and less about knee-jerk grammar rules. And I love having that official resource as great evidence of that.
So whatever you choose to do to boost your score, I'd heavily recommend choosing a program/tutor that would emphasize strategy and reasoning - I've seen lots of people try (and usually fail) to make that verbal leap using "more flash cards" and "more obscure rules and content."
Now, I'm admittedly biased but we've constructed the Veritas Prep program to be heavy on reasoning / higher-order-thinking / strategy (and actually have a full lesson on "Advanced Verbal Strategy" to demonstrate the common ways that the GMAT uses "misdirection" in difficult verbal problems to make you focus on the wrong thing, to hide correct answers so that they don't quite "feel right," and to bait you into falling in love with flawed answers.
If you want to get a preview of how our program might help you, our Sentence Correction video lesson is available for free at
https://www.veritasprep.com/gmat/free-gmat-lesson/.