I think they'll all help the site load faster. Maybe not a huge amount, but they can all help. For the most part the main thing to help speed up a site is reducing the number and size of your images. It's also a good idea to minimize requests to the server.
Far too many sites use images where a line of two of code can show the same thing. Things like solid color background images. Much of the trick is in the site design and knowing what you can and can't do with the code.
So many sites also fail to optimize their images in general. Often simply optimizing an image through phooshop (or any other image editing program) can shave 2/3 of the file size off an image. I've reduced load times on sites by 30 seconds or more just by optimizing images.
is a great site with lot's of helpful pointers to speed up sites.
Even things as simple as reducing white space in your code can shave a few seconds off download times.