I really love my Mesa PH610 but would love to try a Berg 610 to see what all of the fuss is about.
Breaks my heart to say that the NV610 is out of production, although there was a final run of 24 NV610T cabs (T for tweeter), and some of those might still be available. There's the used market of course, but that doesn't give much option for trying before buying.
If you love your Mesa PH610, the NV610 might not be for you. The NV610 is very close to the vintage Ampeg 8x10... point being, it's a sealed cab (no ports), and there's no tweeter. So it'll sound very different from the PH.