Can I Do This With Squid

I currently have a site running on 8 servers : 5 web servers (apache2/php5), 2 DB servers (mysql 5), and one front reverse proxy server.

Currently I use apache as the reverse proxy (with mod_proxy of course).

I have it do 3 type of things:

1) serve some static files (the website's static files) directly from the front server. The files are stored in local directories.

2) cache some other static files (user uploaded images and files) on the front server after downloading them once from the backend webservers. This is done via mod_cache.

3) route some requests to specific web servers depending on a subdomain (on the first few letters of the subdomain more precisely). To do this i use rewrite rules like :
RewriteCond %{HTTP_HOST}^sub1(.*).domain.com$
RewriteRule ^(.*) http://sub1%1.webserver1.com/$1 [P,L]
RewriteCond %{HTTP_HOST}^sub2(.*).domain.com$
RewriteRule ^(.*) http://sub2%1.webserver2.com/$1 [P,L]
etc.

My web servers are not in a cluster from this point of view, so it is important that the reverse proxy is able to route requests based on subdomain like this.

Now I have a few weird performance problems on the front server. CPU, hard disk usage and memory usage keep staying at relatively constant (and always low) levels, yet the server load periodically spikes to places anywhere between 4 and 12 during the day. This seems to be mod_cache related (spikes disappear when i disable it) but I can't figure what's happenning, and I'm reading everywhere squid is a better alternative to do reverse proxying.

Only, I don't know if i can do the same as mentionned above with squid. From what I read, I know I can do 2). However I'm not sure if squid is able to serve some files (based on URL patterns) directly from the local file system rather than querying them / caching them locally ? And can squid route the reverse proxy requests to different web servers based on the subdomain in a URL?