The Avro tests are unnecessarily serializing and deserializing their own schema as part of the messages. In real life both reader and writer would have the schema, readers/writers would store it (once)/read it, to/from the file format, or handshake it (once) on an RPC session.
The attached patch (v1-0001-
CASSANDRA-1765-don-t-ser-dser-schema-string.txt) fixes this.
Results run on my laptop here: https://gist.github.com/2f5d00d87c77260bcaac
These results are averages of the 5 tests ran. One thing interesting about the Avro results is the high/low swing on the serialization times that make up the average. About half the runs are ~2175, and about half ~1200. It'd be interesting to find out why that is, 2175 would make it the slowest by a wide margin, and 1200 the fastest by a wide margin.