GMAT Strategy

Agreed - they don't officially tell us, of course, but these are the hardest questions.

They are representative of some of the hardest quant problems but probably not the absolute highest difficulty possible - I've seen harder questions on the test (but then I'm scoring in the high 700s, so I am occasionally seeing the absolute hardest questions in the pool).

Also remember that you're not going to get everything right - no matter how good you get, the test will give you stuff you can't do. So let's say you can get the 720 level Qs right but you get all the 750 level Qs wrong - that's fine. Your score will still be around 720, which is a fantastic score. As long as you can get most of the questions right at and below whatever difficulty level you're shooting for, you'll get the score you want.