The biggest impact is not to have JS and not to have a giant amount of HTML / CSS. That keeps the content very small. The syntax highlight is rendered at compile time.
There's no JavaScript and only a small number of CSS dependencies. No caching, 239kB transfer. With caching, it's only a 3.1kB transfer.
Interestingly HN's front page is an order of magnitude smaller in uncached transfer size. It does include some JS, but the lower perceived snappiness seems to owe to longer round trip times (for me anyway ~60ms for HN vs ~10ms for dev.l1x.be).
The biggest impact is not to have JS and not to have a giant amount of HTML / CSS. That keeps the content very small. The syntax highlight is rendered at compile time.