It mostly depends on your GMAT goals, to be honest. If, for some reason, you feel that you need to get a 51 on the GMAT quant section, then yes, you probably should be able to handle pretty much anything, including the extra-hard questions. But for most applicants, there's no real reason why you need to be an expert on the hardest quant questions. A nice, balanced 700 might be something like a 47 quant/40 verbal -- and to get a 47 on the quant section, acing the extra-hard questions really isn't important. You just need to execute extremely well on the easy-to-medium stuff, and not get completely obliterated by the harder questions.
If you're trying to figure out where you stand, the GMATPrep exams are usually the best bet. Bunuel's resources are always fantastic, but they may or may not be the right thing for you at this stage of your studies.
Good luck with everything!