I cleared SCJP last november and I had the same doubt/question as you. At that moment I was a little tired of studying and reading, so I preferred to go for SCJD. However, I assumed that going for SCWCD would be faster. A colleague told me he had the HFSJ book which I could use as a preparation. So in the end I chose for SCWCD and cleared it last week. If you don't hate to study then go for SCWCD. It's not hard, it's just a lot of facts/stuff you need to know for the exam. Here is a useful link: http://faq.javaranch.com/java/ScwcdLinks
I cant really tell you whats next from SCJP because you are ahead of me in the race.
But can you tell me what was the difficulty level of the real exam v/s the K&B questions??
And can you also tell me how cramped the codes in question were?? Because in K&B questions codes look really messy(though the author claims that its for preparation purpose). I am a bit worried about the style of code in real exam. Because I find it a bit difficult to concentrate hard and find those NullPointerException,local var not initialized sort of errors(though my theoretical and practical knowledge of the subject is more or less good) but I find it bit difficult to concentrate hard on codes to trace these errors.
If you could reply, then that would help me a lot....