Did a quick comparison with my own service, BitBalloon.

On appengine you're just deploying a dynamic app that just routes everything to a static folder, but since Google doesn't know this is a static site, it's pretty limited what they can do to set good cache headers and optimize stuff for performance. So even if they have an awesome infrastructure, BitBalloon will make your site perform better.

Here's the quick test result from the same site uploaded to AppEngine and BitBalloon:

http://tools.pingdom.com/fpt/#!/vLi9d/http://teststaticsite.... http://tools.pingdom.com/fpt/#!/dwqwvX/http://speedtest.bitb...