I believe that 600 level question on GMAT Club tests
are on that level, maybe a little below. GMAT Club's 700 level questions can be IMO incredibly hard and there are many problems that I cannot solve correctly. Yet when I do the GMAT prep test I score in the low 700s (48q 40v). However, it would be great if you could also practice the 700 level questions because they tend to push you to learn more and improve your test taking stamina. To give you an example from my experience, I took a GMAT prep a month ago and scored 31 in verbal. After a month of doing tough problems and studying diligently I got to 40 and still improving quickly.