I discovered something when I had a job that involved interacting with traffic engineers, and reading the California road design manual. Those yellow spped signs on curves are designed based on visibility. There is a formula that takes into acount speed, stopping distans at that speed, and visibility, assuming vertical obstructions on both sides of the roadway. That is why the speeds seem unreasonably slow to many people.

As far as driving 55. I am as big a tree hugger as anybody, but I drive freeways in Southern CA, and in some sections, you will get run over if you drive 55.