Thank you twistor and seba240698 for supporting my advice on how to study for the GRE Physics test. I invested quite a long time gathering all kinds of tips, information, and advice from websites, professors, and excellent students that had previously taken the GRE Physics test. Though there are a great many ways to study for it, what I wrote above is what I would have done if I had to take it over again and if I only had 50 days to study for it. That, I find, would be the most efficient way of attacking it.
I see that seba240698 gave a complementary note to mine, emphasizing that : "it is true what others have been saying, GRE is a test of speed, more than knowledge or skills". And it's true the GRE Physics is about applying the basic principles of undergraduate physics, but FAST. For this, there is nothing better than practice and reviewing, and specially practicing under real-timed conditions to gain SPEED.
So, regarding twistors questions: yes, I can be sure that the next tests will be most similar to GR0177, since I took the GRE Physics twice, and friends that had taken it before, and others after I did, described that GR0177 was BY FAR the most similar in style to the actual test. It is a fact that the ETS test committee does not have great creativity and that they will recycle the problems from past ETS facsimiles. So, no, they don't "change it around". And yes, THERE IS less of an advantage studying the other tests (GR8677, GR9277, and GR9677), since those tests have practice problems that are not as similar to the practice problems in GR0177 compared to the actual test. In other words, I would first prioritize the practice and study of principles behind the problems of GR0177, then, if time permitted, I would go on to GR9677, then GR9277, and finally GR8677. Studying problems from other places is not a bad idea, but not the BEST way to practice. In other words, my advice shows how to OPTIMIZE that study and practice time under a limited time frame (around 2 months before the test).
This will definitely be my advice for my fellow buddies that must take the test soon and for those who will take it in the future.
