[rodgerd]

> I'm guessing part of the appeal will also be super-wide bandwidth between the cores.

If it's anything like previous-generations, that will be infiniband between books. The benefits on Z-class systems tend to be very big per-core, per-socket caches and, as the person you're replying to said, a lot of internal redundancy and automated failover (multiple backplanes with failover, spare memory and cores with failover, and so on and so forth).