Hi vrn2vw.
It looks as if the way for you to go is to get a few more points out of verbal and way more points out of quant.
Given that you finished both sections so early, one thing that will clearly help is just getting better at handling the pacing of the test itself. You were blowing through questions way faster than you had to, and had you been more careful likely you would have gotten at least a few more, if not many more, right in each section. I personally find that my level of care in verbal makes a huge difference. So who knows, maybe just by changing pacing you get to V48, or higher, and with that Q40, at which point you would already be at 710.
One way to get better at pacing is just to play the game by taking more CAT's. You could buy a set of CATs from Veritas or Manhattan Prep and not necessarily even take the test under realistic conditions. The idea is to get better at handling the sections, and it can even be helpful to focus on one section at at time. I have seen someone recently make great progress by buying a set of CATs from which one can choose sections and just taking quant CAT after quant CAT, taking one daily even, and playing the quant section like a video game.
At this stage you might even get use from PowerPrep, the official GMAT software that came out before GMAT Prep. Yes you may see some questions that you have already seen in the Official Guide, and SC has evolved since that software was created, but generally the tests are pretty much like the actual GMAT, though they don't have IR sections. You can download PowerPrep from here.
https://www.beatthegmat.com/mba/resources It's not that popular, but it can be super useful and I think for your current purposes it could be just right.
To get better at quant, go though and see what you don't know how to do very well, and then work on each of those areas, mastering them one at a time. Each one you master is roughly good for another point or two. So by getting better at a dozen things probably you get your quant score into the upper 40's.
One way to master quant topics is do searches on each to learn about them. For instance, you could search on "gmat probability questions" and find all kinds of discussion on how to handle them. Then you could go to the GMAT section of
https://bellcurves.com/, sign up for a practice account, and do questions in that topic area until you achieve a high hit rate and rating. Then pick another topic area and do the same thing.
Often when you are doing practice questions, it makes sense to do them as slowly as you need to in order to get them right. If it takes ten minutes, or a half hour or more at times, to get to the right answer to a question, go ahead and do that, as in doing so you will be developing the hacking skills necessary for getting question after question right on the actual test.
Given your current score on verbal, I guess you don't need to learn too much more about it. Probably you could learn a few more SC concepts and other than that just learn to better see what is going on in various GMAT verbal question situations. In RC maybe you need to get a touch better at making sure that what the answer choices say matches what the passage says. In CR, maybe you could get a little better at not getting smoked by trick answers that seem relevant and are related to the prompt but don't truly answer the question. In SC I am guessing you could be better at noticing how the parts of the sentences work together, or don't. SC success is so much about hacking. If you have a decent grasp of the English language and can hack well, you should get most or all of SC right. Also, there are often multiple decision points in an SC question. So if you are not sure about one, you can often just look for another and get the answer.
One way to get better at verbal is look over questions you didn't get right and ask yourself, "How could I have gotten this one right?" What could you have seen and used to get to the right answer?
So there are some ideas. 750+ should not be too challenging for you to achieve. Just get better at the GMAT game, maybe partly by playing it a lot, and make it happen.
