How have you actually studied those problems? Doing them is not the same thing as learning from them. :) You don't really learn from them until you pick them apart after you do them. So doing new ones won't help much if you don't learn from the ones you already did.
This describes how to learn from them:
http://www.manhattangmat.com/blog/index ... -the-gmat/First, go learn how to learn on some OG problems you've already done.
Then you can do new problems to test yourself. Have you done both OG13 and the Verbal Supplement? If so, then I'd go to the GMAT Prep Question Pack - it contains about 200 verbal (and 200 quant) questions and you can set it up to give you problem sets. You could tell it that you want, say, 8 problems across SC, RC, and CR, chosen only from the medium and difficult buckets.
And then dig in and analyze them in the same way you analyzed the other ones!