I compared the rankings and they seem to be the same, the old rankings loaded in 0.20 seconds and the new ones loaded in 0.09 seconds. So I think this is just a way to speed up searches and reduce waste of resources. Makes sense since "Caffeine", as per Coffee, is supposed to speed you up more.
This was stated a long time ago, that only one DC was using caffeine as a test / benchmark, not one person has come out and said otherwise, and they have disclosed which datacenter was using caffeine, This is the IP that produces Caffeine results: 50% of the time: (that's what Matt Cutts says not me) CAFFEINE DATACENTER IP: http://209.85.225.103/