Exactly. The start of the push will already consume downstream bandwidth until it's canceled by the remote side. I guess in the worst case it consume about up t

Exactly. The start of the push will already consume downstream bandwidth until it's canceled by the remote side. I guess in the worst case it consume about up to the maximum window size of the stream (typically 64kB). The "classic" approach compared to that is the client initiating another GET request for each asset after it has received the index page. This requires more upstream traffic. However the webserver could directly respond with a 304 for cached assets, which means less downstream traffic.