All in all, I found Silk - especially the newer versions - to behave like a pretty standard WebKit browser. Some of Apple's specific settings do not exist, so testing on Chrome on the desktop was the closest experience (although one of the caveats is that Chrome seems to be taking webkit fixes faster)
I did not see anything that could indicate that fast browsing does something different for content hosted in EC2. Since hosted content often comes from a number of sources, I do not expect them to share traffic on internal or external networks, although it sounds like something worthwhile on forums on forums.developer.amazon.com/forums/category.jspa?categoryID = 3 to get an official answer
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