Sun is planning to take off the old exam (I think towards the end of this year - not sure) and replace with the new exam. So, you should still be able to continue and finish off the rest of the exams within that time frame.
Now, your question - whether to stop working on SCEA-4 after doing the part-1 or not !!!
This simply relies on your objective of WHY you need to do the SCEA exam. Is it something to show in your resume that you are sun certified architect with the latest version? Then stop working on 4 and move on to 5. But if I were you, then I would try to finish off the older one which I have already started and do the upgrade. The knowledge that you acquire from the exams/assignments can then be applied to the work that you are doing, and gradually you become a "fully qualified" Architect- both theoritically and practically. Also, bear in mind that many industries are still in the process of switching over to the newer versions, which can still take a few years from now. So you might be still working on the older versions.
Being said that, please check whether you can still purchase a voucher for the other two parts of the exam !! http://www.sun.com/training/certification/java/discontinued.html
[ April 27, 2008: Message edited by: Giju George ]