We are trying to improve further the speed of some sites with older HTML in order as well to obtain better SEO results. We have now applied some minify measures, combined html, css etc. We use a small virtualized infrastructure and we've always wanted to use a light + standar http server configuration so the first one can serve images and static contents vs the other one php, rewrites, etc. We can easily do that now with a VM using the same files and conf of vhosts (bind mounts) on apache but with hardly any modules loaded. This means the light httpd will have smaller fingerprint that would allow us to serve more and quicker, have more minSpareServer running, etc.

So, as browsers benefit from loading static content from different hostnames as well, we've thought about building a rewrite rule on our main server (main.com) to "redirect" all images and css *.jpg, *.gif, *.css etc to the same at say cdn.main.com thus the browser being able to have more connections.

The question is, assuming we have a very complex rewrite ruleset already (we manually manipulate many old URLs for SEO) will it be worth?

I mean will the additional load of main's apache to have to redirect main.com/image.jpg (I understand we'll have to do a 301) to cdn.main.com/image.jpg + then cdn.main.com having to serve it, be larger than the gain we would be archiving on the browser?

Could the excess of 301s of all images on a page be penalized by google?

How do large companies work this out, does the original code already include images linked from the cdn with absolute paths?

EDIT Just to clarify, our concern is not to do so much with server performance or bandwith. We could obviously employ an external CDN server but we have plenty CPU and bandwith.

Our concern is with how to have "old" sites with plenty semi-static HTML content benefiting from splitting connections for images and static content via apache without having to change the html to absolute paths (ie. image.jpg to cdn.main.com/image.jpg happening on the server not the code)