Do the sizes of different types of file have any impact? For example, does a 50kb image have more impact than a 50kb JavaScript file? (I'm guessing yes, since the js file will tend to be compressed for sending, whereas the image is already compressed)

How about the use of cdn for common files? Is there a correlation between, say, the use of Google's jQuery cdn service and faster/slower sites? What about distinct domain lookups for multiple files? Is rakuten loading all those files from a single domain, while Google spread the 10 requests around a pile of specialist static file servers?

It's interesting data though!