If the questions are easier in the supplement books than in the OG, how is this helping a high scorer?
Wouldn't you just see such difficulty level questions only during your first 5 on the Q section? And then once you answer those correctly, you'll suddenly start getting way tougher questions that you are not really prepared for....Like someone else suggested, keep re-taking the GMATPrep tests and you'll be seeing the right questions for your level.
As far as the V section goes, I am not entirely sure but it seems to me 90%+ of the questions in the OG and V suppl books are already in the 1000 sc, rc, cr documents that you can download here.