I cleared OCPJP 6.0 (1ZO-851) With 85% on 28th July 2012. I studied from Kathy Sierra exam guide for about 2 months. As I am a working professional I could spend only 1.5 to 2 hours daily.
Following as well were helpful and confidence booster:
1. I had given tests twice on www.scpjptest.com scoring 80-85 each time before appearing for the actual test. It is a very good free test site and it gives you the detail analysis of your weak and strong areas.
2. I had one test from sjpcp 6.0 cd exam. But I could score only 70% there. I suppose its little tougher.
The time provided 2:30 hrs is enough to answer all the 65 questions and then review(unanswered and marked) them as well.