An alternative example...
http://www.aerospike.com/blog/big-bucks-for-bluekai-snapdeal...
"Snapdeal replaced 10 MongoDB database servers with the Aerospike database on two servers on Amazon EC2—an 80% reduction—while continuing to rapidly scale the business."
Critical thinking includes not suggesting that someone should prove a negative. Those are independent benchmarks with the sole 'violation' of being re-posted on the vendor's site. Unless you can provide metrics that disprove them, they stand.
It's an example case from a customer of the database vendor. I'm unlikely to find anything better until after people start playing around with the open source version.