Hi shere676, first off, congrats on getting 700 on GMAT. I can see how you'd like to do a re-take and I believe that if you can raise your score up by at least 40 points (740 or more), you should go for it. You mentioned MGMAT's strategy guide, did you do all 8 of them? Make sure you do the MGMAT SC
to help you out on the sentence correction portion as it seems to me that that section is giving you a rough time.
I, too, have found the real SC questions are a bit tough. I don't remember if it's scientific or what, but I did remember struggling with SC on the real GMAT when I can easily pick off some answers when practice. I attribute that to probably a lack of foundation and a huge boose in time pressure. No matter how you prepare, you'll never be able to imitate the same atmosphere as you'll experience in the test center...since every question in the test center counts, you will feel more pressure (human nature). However, just try to relax and make sure you follow your foundation. If you're naturally good at SC, follow your gut feeling because chances are, after practicing for so long, you probably know the right answer but are just doubting yourself. Understand that your verbal score (V37) is pretty high (I think it's 80 percentile), so it'll be even tougher at this point to try to raise that. But once you set a goal, go for it! As long as you know it's realistic, no one should stop you. Sorry, I think I've digressed from your main question,