I reroute certain websites through a proxy with a proxy.pac file.

It basically looks like this:

if (shExpMatch(host, "www.youtube.com"))
    { return "PROXY proxy.domain.tld:8080; DIRECT" }
if (shExpMatch(host, "youtube.com"))
    { return "PROXY proxy.domain.tld:8080; DIRECT" }

At the moment about 125 sites are rerouted using this method. However, I plan on adding quite a few more domains to it, and I'm guessing it will eventually be a list of 500-1000 domains.

It's important to not reroute all traffic through the proxy.

What's the best way to keep this file optimized, performance-wise ?

Thanks