If you have a job at the moment than wait, because certificates are usually useful when you are looking for a job. If you don't have a job, you can go for the 4th edition, because I assume finding a job has higher priority than getting a one level higher certificate.
A different view: according to google the difference between the 4th and the 5th version isn't that significant and the 5th contains the 4th. Let's assume that you have PMBOK4 and you meet somebody who actually knows what PMBOK5 is. She will also know the difference, and that you are familiar with the basics (you have PMBOK4) and only a small "upgrade" is missing. If you meet somebody who has no idea what PMBOK5 is, will look for a certification with the higher number, but would you like to work with somebody like that? Maybe not. Following this logic, PMBOK4 is enough.