In general I agree that you should err on the safe side and do HTTPS everywhere. But, until you profile your site with/without HTTPS how do you know performance reduction is minimal? Do you have evidence to support such a blanket argument?
> 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...