Congratulations!
You are right about the preparation materials that are available now for SCJP 5.0.
The primary arguments for taking SCJP 1.4 that I know of are:
It is a lot easier. I took SCJP 1.4 in 2002 or 2003 and got 96 %. My skills are 100 times higher now, but in mock exams from whizlabs I get less than 80 % for SCJP 5.0.It is said that the questions are ambiguous, as a consequence to the new "performance based" style. The 1.4 questions are quite directly based on the JLS and API specification. Thus what is right and wrong in SCJP 1.4 is objective. Most people are not aware of the difficulty of SCJP 5.0, so they don't give you the deserved credit for passing it. I sometimes meet people who are nagging about my SCWCD 1.4 score of 88 %, claiming that most people get over 90 % there, often 100 %. Apparently they get it confused with the old SCWCD exam.
I still think that SCJP 5.0 is the better long term investment. SCJP 1.4 will slowly start to loose its value as soon as it cannot be taken any more. My impression is that such an IT certification looses half of its value within 5 - 8 years, starting at the day when it cannot be taken any more. As a potential employer, I would give you quite some credit for having SCJP 5.0 even today, because it is very useful to have someone on the team who is fluent in the most important JLS and API changes in Tiger. Being up to date rather than doing things the 2005-way is considered an important attribute of an IT-professional. The full advantage of knowing the new Tiger features is yet to arrive with
EJB 3.0.
Kai