I see a surprising number of tutorials on blogs recommending 4096bit keys and I do wonder if people know just how much extra load that is. A properly set up HTTPS site with 2048bit certs will be pretty fast - about the same as HTTP and your time will be better spent optimizing other things like images.

For anyone curious about how much slower try "openssl speed rsa2048 rsa4096" for a quick benchmark. The results are ugly.