I don't get it. Given that most websites have some dynamic content, that static assets can be updated, edited or otherwise altered at any time, Google must be fetching content on a request-by-request basis, i/e acting as a proxy. How can this be faster? You've got the existing latency of fetching your content, PLUS the extra latency of Google zipping and concatenating assets and forwarding the result on to the client.
Doesn't make any sense.