I have a pretty big JavaScript file here which I want to embed into my website. The HTTP server is smart enough to GZIP the file before delivering it to the browser.
The HTTP headers sent to Safari say it's compressed (It has the Content-Encoding: gzip header, and it says the Content-Length is 119406 bytes) - I'd trust those more than the bold number saying 430.61 in Web Inspector. How it determines both those numbers in the top column, , I don't know.
You can get verification on how many bytes is going over the wire if you sniff the HTTP request with wireshark.