Also, don't forget: if you don't have the performance you want yet, you aren't done with OG. You actually have to study those problems, not just do them. See this post for some ideas about the kinds of questions to ask while you're analyzing a problem:
http://www.manhattangmat.com/forums/no- ... 89-30.html
Look towards the bottom of the third page (this link should take you to the third page).
Another place to get quant problems of all types: GMAT Focus. These are also official, retired test questions that do not overlap with OG in any way. (GMAT Focus is a paid diagnostic test from the makers of the real test - go to
www.gmatfocus.com for more details.)