What limits Postgres performance when the whole database lives in cache?

Re this talk given by Michael Stonebraker:

http://slideshot.epfl.ch/play/suri_stonebraker

He makes the claim that in a modern ‘big iron’ RDBMS such as Oracle, DB2, MS SQL Server, Postgres, given enough memory that the entire database lives in cache, the server will spend 96% of its memory cycles on unproductive overhead. This includes buffer management, locking, latching (thread/CPU conflicts) and recovery (including log file reads and writes).

[Enough memory in this case assumes that for just about any business, 1TB is enough. The intent of his argument is that a server designed correctly for it would run 25x faster.]

I wondered if there are any figures or measurements on Postgres performance in this ‘enough memory’ environment to support or contest this point of view?

Regards

David M Bennett FACS

Andl - A New Database Language - andl.org