Should I do 700 Questions while still getting 50% of 600s wrong?

Dear iliavko,

I'm happy to respond.

My friend, here's what I'll say.

First of all, I am extremely skeptical about the assigned question-levels, on GMAT Club and elsewhere. See my rant on this here:
Is this a 700+ level GMAT question?
It's not at all clear to me that a batch of question is legitimately at the 600-level simply because GMAT Club or someone else deems them thus.

Nevertheless, for the sake of answering your specific question, let's assume that these dubious question levels are well-defined. If you are getting about 50% right at a certain level, this means (a) this is approximately your level, the level at which you would test today, and (b) you focus your practice here, because this approximates the majority of questions you would see on test day, assuming you are still at this same level.

It's certainly not useless to practice much harder questions. It's always good to challenge yourself. These harder questions shouldn't constitute the majority of your practice, but practicing some is fine. It's quite possible that you will learn techniques and strategies in these harder questions that make questions at your level seem easier. What's extremely important with all practice, and especially with the occasional practice of harder questions, is that you study the solutions thorough. Ideally, you will keep an error log to help consolidate your learning. See:
Studying for the GMAT: Learning from Your Mistakes

Does all this make sense?
Mike