> I'm exceptionally skeptical of those claims

I can attest that these guys are known to post bogus benchmark numbers. The claim on their home page ("4x faster than Protocol Buffers in this test!") is incredibly misleading; their benchmark is set up in such a way that Protocol Buffers are copying the strings but Message Pack is just referencing them. It's true that the open-source release of Protocol Buffers doesn't have an easy way of referencing vs. copying, but it is still highly misleading not to mention that you're basically benchmarking memcpy().

One of these days I'll re-run their benchmark with my protobuf parser which can likewise just reference strings. I am pretty sure I will trounce their numbers.