It's too early for a final verdict, it's still a pre release, not the finished product yet. It is quite stable, a lot more stable than Vue5 when it was just released. There are still issues ( radiosity, hypervue),  and  memory leaks are being eradicated with every new update.
It renders faster than Vue5 if you don't use the new spectral atmospheres ( but you will want to use them!), the new fantastic area lights, and texture filtering ( smoothes out the render, avoiding the hard edges we had in previous versions)
Radiosity (while acting a little strangely right now) is so much faster than before.
Many many improvements and new functions, it's an incredibly powerful program.