INterestingly, Charting Outcomes for IMG's doesn't actually answer your question. They have graphs for Step 1 and Step 2 CK. Both of those show that for candidates who take 3 attempts to pass, the chance of matching is about 10%. For CS all that is listed is an average number of attempts, which isn't all that helpful. I expect that the outcomes might be worse for CS attempts. Bottom line is that you've dug yourself a very deep hole, and there really isn't a way to fix it. You can't apply this year with two failed CS's, so you'd need to take it again, pass, and then apply next year. Your chances of getting a spot are very poor. Only you can decide if it's "worth it".