>NVidia Titan GPU : it is a relatively cheap, massively parallel GPU

Relatively cheap compared to having to build clusters, perhaps, but $1000 isn't cheap for a desktop computing GPU.

A mid-high tier card (GeForce GTX 770) is closer to $400. A mid-range gaming card (GTX 760) is closer to $260.

Those finding the topic link interesting may also be interested in this CUDA radix sorting article[0] from 2010, as it featured "one billion 32-bit keys sorted per second."

[0] https://code.google.com/p/back40computing/wiki/RadixSorting