Having a hard time with the hard OG problems in CR

Hey guys, Im doing really well in the OG questions in CR up to about number 80, almost 95% correct but after that when I hit the hard problems I go down to about 50% correct and it is really pissing me off to loose such accuracy so quickly.

Its obvious that I need more practice with tougher questions, but aside from the OG where can I find a bank of questions that focus on JUST the hard 700-800 level questions. I know that GMATclub has a question bank and wanted to know what people thought about taking that route to get more practice questions.

I've done the MGMAT questions so that resource is out.

Thanks guys