hi tlntd42,
I'll try my best at answering these:
1) the
Manhattan GMAT (supposedly different from
MGMAT, whatever that is) CAT are VERY different from GMATPrep. I was pretty surprised when I first took them. Their Quant section is TOUGH. I got almost all 700-800 level questions even though I missed 3-4 in a row. The questions generally take 3-4 minutes to solve if you're not perfectly used to them, and I found myself with only 10 minutes for the last 10 questions, forcing me to guess. My Quant score in GMATPrep was 50, and it was 44 for the
Manhattan GMAT.
the good news is, even though I missed 18 questions (versus 9 on GMAT Prep) on the
Manhattan GMAT CAT, the scoring is very lenient, and if I didn't run out of time in the end, I probably would have gotten the same score for Quant.
Verbal was very strange, but some forum people have mentioned that the real GMAT test is trending towards what
Manhattan GMAT CAT presents. A lot more bold face CR, longer RC, and full sentence (3 lines) SC. They were tough, but my score was somewhat similar, 41 vs 44 on GMAT Prep. But I agree that the logic and the way they ask questions are different from GMAT Prep.
2) I HIGHLY recommend
Manhattan GMAT's Sentence Correction Book. It's $26 off Amazon, but it's very good as it teaches you the most commonly tested grammar rules, refers to the OG11 for practice problems, and gives you 25 more SC CAT questions on their website. I'm more than 1/2 way through the book and it has helped me on numerous occasions to pick the right answer when I narrow them down to 2. The hard part is you have to remember all the rules and what to look for, so practice practice practice!
3) Yeah, same here. I would say do more questions so you get used to the format and you know the equation/technique to use down cold. Then spend an extra 10 seconds at the end of each question double checking what the question was asking for, and if you answered the questions. I think after making enough of the careless errors, I started to check things like "a side of a square is the perimeter divided by 4, not 2" and "x > 9 means x cannot be 9" and stupid errors like that. Other than that, I'm in the same boat trying to figure out how to reduce my careless errors.
4) Well, I have 2 weeks to go, and you're way ahead of me. I would get
Manhattan GMAT SC book and go through that, even though you've done the
OG book already, it'll help you focus on looking for the SC errors and reinforce the education. Maybe some of the GMAT Club Challenges (I haven't done any nor do I think I'll have enough time to) would help.
Another benefit of getting the
Manhattan GMAT books is you get access to 6 online CAT tests. Those quant sections will kill you because of how hard they are, but you'll learn a LOT of tricks when it comes to consecutive integers, rate/work problems, prime factors, and things like that.
Other than that, try to read RC faster and look back in the passage for answers after you read the questions, that may save you some time in verbal. Check and double check common math errors. Do a lot more CATs to improve timing. That's all I can offer for now. You definitely have a lot more prep and practice than I do at this point. Good luck!