I wish I had more solid data. Cloud Spanner claims about 10K read QPS and 2K write on a "node" which costs $1/hour. The Spanner paper reports about 10K read QPS per core. As I understand the cloud deployment it's 3 replicas at that price, so $0.33/hour should buy me about 8 cores and so I'm not sure what the disparity is (maybe markup? CloudSQL is 2X the cost of compute), but I'll go with 10K QPS/8 cores at the low end. Anyway, something like 500-1000W for ~100 cores so something between 100 QPS/W and 10 QPS/W using the 1000W and high and low performance estimates, or 10^15 / 86400 = 11.6e12 QPS for somewhere between 116MW and a a little over a GW. Sounds comparable(?) to MySQL+TAO on the low end to ridiculously expensive at the high end.

EDIT: I have no clue how efficient MySQL+TAO really are but figure that at least tens of thousands of machines go into it.