I don’t know of any performance metrics for pubsub specifically, but I doubt that it will publish to 100000 subscribers in a second. This is mainly due to the fact that the publishing is currently single threaded. There is actually a note in the code that says that this should use multiple threads (which it very much should). It is a fairly simple improvement, but it hasn’t been done yet.
As for the cluster, pubsub does not yet work in a cluster.