Apart from that, my idea of what every web dev should know about HTTPS is use HTTPS for everything. The performance reduction is minimal and far less important than the security gain...
You've got extra overhead to setup the connection, extra processing to handle the encryption, no intermediate caching AFAICT. Clearly that has some impact - I'd expect it to be significant.
> On our production frontend machines, SSL/TLS accounts for less than 1% of the CPU load, less than 10KB of memory per connection and less than 2% of network overhead.
> If you stop reading now you only need to remember one thing: SSL/TLS is not computationally expensive any more.
1. https://www.imperialviolet.org/2010/06/25/overclocking-ssl.h...