I don't know if this will work for everyone, but I unplugged my modem and re-started Steam in offline mode. After that, loading times were cut in half and all of my previous crashing, stuttering and freezing problems disappeared.

I bought the box edition, not the Steam version. I had few problems until about twenty hours in, then started having lots of random crashes. I have to leave the modem unplugged while I play, or the problems come back.