underdog
Where can I find the most challenging and difficult yet an appropriate compilation of Quant (PS and DS) and Verbal (RC, CR, SC) Questions?
Basically, I am looking for a high quality compilation of 700+ GMAT questions that I should work upon after completing OG12, OG10, the OG Quant Review and the OG Verbal Review; but before starting with the practice tests.
Perhaps it would be best to drop the OG 10 and just stick with OG 12, OG Quant 2, and OG Verbal 2. That's plenty. These three guides are necessary, but insufficient to bring you up to a 700-level performance. After you've successfully completed these, it's time to move on to harder material. There's no need to do more OG, except for the GMATPrep (but that's more for your diagnostic and test practice rather than question practice).
I have already provided a list of hard quant problems for you in
another thread. If you're looking to buy materials, then
GMATClub Tests and Sackmann's Extreme Challenge set are great options.
Regarding verbal, look into
LSAT sources for hard RC and CR practice. For SC, the
Brutal SC document is pretty difficult.
And remember Pavle's advice above.