I think it's a good number for a sustained load within a large cluster.

50MB/sec multiplies due to replication and consumers. Also in large clusters, the bottleneck comes often from the network switches rather than the rest of the stack.

Also when it comes to sustained load, many people don't realize that 50MB/sec × 10 brokers × 24 hours × 7 days × 3600 seconds leads to 300TB per week (without counting the replication). :)