Problem is, Silk isn't marketed as just another browser. To see its effects, you have to use it like Amazon intended for it to be used. You don't disconnect the batteries from a Prius then say it's less efficient than a standard car just for the sake of being "fair".
Caching turned off is for cold-cache test. Storage is relatively small on tablets and it's very plausible to get a cold cache first pageload.
Steve is pretty good at these kinds of tests.