I wanted a GB5 Custom for a long time (still do, actually, but I have put a limit of 3 basses on myself).
I DO, however have a Cort Artisan C4 2004 LTD with humbuckers (not the same as the A5, but still...) That bass is my main bass (I guess it's the wenge neck that does it for me).
I find it to be very versatile, BUT lately I have been wanting to try a P-type bass, and classic rock is one of the reasons for that. There is something about that P-pickup that cuts through the mix in a way that you have to work with EQ and effects to get right with a J-type or a humbucker type bass like the Artisans.
I guess I have been looking at Cort basses for a long time without finding that perfect P-bass, and having a Cort Artisan as my main bass, and I adding a second doesn't make much sense to me. The A5 will surely be an upgrade from your V-DLX, but it will be better within the same type of bass. Sure, the A5 have more bells and whistles and better wood, electronics and parts, but it is still the same family of pickups and body shape.
I guess you should ask yourself: Do I want an upgrade of what I have, or do I want something different?
If you want something different, and a Cort, I'd go for the GB5, otherwise the A5. And running the risk of swearing in church (I DO love my Cort bass): You should also consider a P-type bass if you play a lot of that classic rock, and then you need to look at other brands. The new Squier VM models have a lot to offer, and I sometimes wonder if Cort factories play a part in some of those models...

I understand you want a 5 string, and then I think this is an interesting model:
Invalid Link Removed (I am a 4 string bass player myself)
Edit: Since I mentioned my bass, I guess I can post my picture of it, too: