I work on a site with a long history. I recently created a benchmark and found that I could make around 500 synchronous HTTP requests to our infrastructure per second (essentially localhost calls). If I switch my benchmark to HTTPS I can only make about 5.

That's a big difference. I'm a developer, not a hardware guy, so I don't know what causes the slowdown for us. I assume it's the actual setup and teardown of the HTTPS connection. That is a fairly significant difference when I want to use API's via HTTP/HTTPS and I need to make a lot of calls quickly.

My point is that HTTPS still seems to be 100x more computationally expensive than HTTP.