1. If you're starting now, I'd recommend you to go for 5.0. 3. There's no exam oriented book yet. Please check the SCBCD Links for resources. And good guess, there's no Head First, and probably will not have one soon.
I'm not so sure that the new exam is the only way to go. When we made the new exam, we decided that it would NOT be a superset of the old exam. In other words passing the new exam doesn't prove that you know old style EJBs!!
So, if your company is using the new style great! But if your company is using the old style EJB then the old exam is still valid. I would guess that the old exam will be around for many years and that many companies will be slow to switch to the new stlyle of EJBs.
Long story short, find out what your company is doing before you decide!
Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)