The other two databases you mentioned are not in the same problem domain. Redis will not manage more data than it can address in memory (barring the deprecated virtual memory paging) and Memcached doesn't bother with persistence at all. Both of these are very much memory databases targeting ephemeral storage tasks. Neither of them have distributed capabilities beyond very minimal master/slave configurations.
The YCSB benchmarks [0] were developed for Yahoo to evaluate a wide range of NoSQL databases by abstracting a few common operations to measure the primitives shared by all of them.
I have started work on scavenging parts of @tiborvass's library to make a more minimal and maintainable Go library, but there are other projects between me and completion. :)
Also for the Cassandra benchmark, was caching turned on for the data column family in the usertable keyspace?
Additionally it would be great to see the operations per second for the "load" portion of workload A as this represents a 100% write workload.
Other than those few points HyperDex looks pretty cool and has some great read performance.
