I'm in the same situation as you, jonatande. Since the 5th edition has the same quant information, I'm going to keep the 4th since I'm a lot stronger in Verbal (by a wide margin). I took a practice test which only confirmed it.
I think if you take a practice test (doesn't have to be GMAT Prep, IMO) in addition to waiting for other reviews about the differences between the 4th and the 5th, you can make a better decision.
Also, I actually have the all the Veritas and
MGMAT 4th books, plus the PowerScore Verbal Bible. I looked at the PowerScore Verbal vs the
MGMAT Verbal books and I think I like PowerScore's better. If you do require additional verbal help, that may be a better option for you too since I think that book is under $30.