GMATPrep is great to measure your score and build your stamina. But GmatFix Solutions Engine has more than 1000 GmatPrep problems categorized and in a searchable database with answer explnations (with 600+ video explanations).
It takes a matter of seconds to extract all GMATPrep 600-700 and 700+ (or any other level) questions on any category and subject - no more taking GMATPrep 11th time to extract all questions.
My GMAT is scheduled in a week, so alas, I would not have much time to prepare with GMATFix...I wish I had discovered it earlier. For about 25c I could get access for two weeks - can't beat.
p.s. I have no affiliation with GMATFix. I just thought discovering this in time may help fellow GMatters.