770 (Q51, V44) - Don't let non-GMATprep tests get you down

Hi everyone! Because I had my GMAT yesterday and found the debriefs really useful during my prep-phase, I thought I'd give a short overview of my experience and my 2 cents on the whole prep-treadmill and the different materials I used. I didn't think I would write this much, so just skip to the materials I used if you want the main point of my post.

Background
I'm an economics student and second-language English speaker (though I spent all of high school in an English school and study in England). My diagnostic test with GMATprep 1 came out at 730(Q49, V42) in February and I spent about 150 hours studying on and off spread out over the course of about 4 months while I was at university. Because the average GMAT for a program I'm interested in is about 740, I decided to set my sights for 750+, so my prep focused on this.

Brief summary of test experience:
Everything was pretty normal, the part most worth mentioning is quant: quant went horribly, or so I thought. I found that the questions jumped around a lot in difficulty. I would have a GMATclub 700 level question and next something much much easier, so I was really worried I was getting everything wrong left and right. I was very unsure about my answer for a sizable portion of the questions and felt I was failing to consider something in practically every DS question (my main weak point in the GMAT). It felt like one of my worst performances compared to all my practice exams and I actually considered cancelling my score because of this: obviously I'm very glad I didn't. I had only gotten Q51 on one previous full practice test.

Materials Used
So here's the actually interesting part of my post:

GMATprep Tests: by far the best and most accurate gauge and estimate of your test-day score. I took each test twice and got 770, 760 and 780 after practicing which are very close to my actual scores. The quant and verbal scores were off my actual test by max. 1 point in each test. The third test with 780 was a little amplified by the fact that there are not that many high level verbal questions, so practically the entire verbal test I had seen before.

GMATclub tests: really discouraging at first (getting 42nd percentile on the first test is not fun) but with time you learn to master these questions. These are much better quality questions than MGMAT. They are really hard and also a bit harder than the hardest questions in the actual test, but they don't rely on cheap tricks like lengthy computation or way too many cases to make it hard. They also really get you to consider all the possible cases in DS, which for me was very valuable. Usually there's a quick solution, you just have to learn to see it. Absolutely recommended if you want Q50/Q51.

OG 13: not good for theory or high level prep, but very good quality questions to practice your speed on. Even if you only do the hard questions of every section, you are unlikely to be challenged if you are aiming for 750+. If you are already in 700+ territory, I would skip everything but the last ~1/3 of the questions in each section, unless you have particular weaknesses in a particular question type (like me with DS).

GMATclub iPad app: Excellent companion for timing yourself on the OG. Also presents the forum's huge number of questions in a very nice portable way. If you have an iPad, I really recommend this.

MGMAT Math guides: I went through all the math guides over the course of about 2 weeks. Even though I thought I was relatively good at math, these guides gave me a lot of absolutely crucial knowledge for the quant section that I had simply not worked with for a long time. The exercises are not worth it though, they are not in GMAT format and it mostly felt like a waste of time to do them. GMATclub's math book would probably have sufficed for this or would have been even better - for free.

MGMAT verbal guides: SC was fantastic. I went from getting over 70% wrong on SC to consistently getting 75-80% right on practice tests. Probably the single biggest improvement. I hardly looked at the other 2 because I was focused on quant and hadn't had as much trouble in CR and RC. I think reading the economist/FT or NewScientist and the like regularly make CR and RC much easier than any guide book every could.

MGMAT Advanced Quant: probably the single most useful book to me. Though I didn't learn anything new in terms of theory, this guide teaches you how to think your way through those tougher 700+ questions. The strategies and tactics for DS and the emphasis on a systematic approach that you apply to every DS question helped me the most. The 150 practice questions in actual GMAT format are excellent practice and of significantly higher quality than MGMAT CAT questions in my opinion.

MGMAT CATs:
These get an own section because I was really disappointed by them. Overall they are a very mixed bag. I am really surprised these CATs get so much praise on GMATclub. If they really are the best gauge for your test-day performance after GMATprep, the other options must be abysmal. I did 5 of these tests and my scores jumped heavily between 700 and 780. My quant score varied between 45 and 51 and my verbal was even worse, crashing from V48 to V37 literally two days later (no test fatigue or tiredness affecting these results).

I went through the detailed breakdowns of how the algorithm seemed to rate me and it seemed quite messed up sometimes. I could be on 98th percentile for 15 questions straight near the end of the test, accidentally get a question wrong and crash down to 75th. Getting back up however only seems to happen in small increments of 2-3%. So if you get a 600 question wrong near the end, even if you got 15 700+ questions right, you might still end up with a low score.

Additionally, I found that the MGMAT quant questions are often hard for the wrong reasons. While the official GMAT questions need you to think outside the box a little to get the right answer and that is their source of difficulty, the MGMAT questions often rely on heavy computation or too many cases to consider in 2 minutes to make them hard. The verbal questions also felt very convoluted sometimes, and on the CR questions I was often not convinced of the reasoning behind the official answer. Passages are heavily skewed to the 60~ lines variety, which is not really representative of what you'll see on test day I think. Overall maybe good for making you a little humbler in your targets, but really bad for confidence and not a good measure of actual test-day ability in my opinion. Stay away from these in the last week of prep I would say, lest you ruin your hard-built confidence!