Starting Ct5 would be ok. Just be clear you intend it for September so you don't put too much into it at the expense of the 2 you have put yourself in a good position. Ct5 has relatively straight forward notes but time consuming questions. It would be great to try to get your preparation soon into trying to develop the speed required to finish this paper. I think most people who fail Ct5 simply don't finish the exam.
Best wishes
Last edited: Nov 30, 2009