• uninstall nginx-full from wheezy (nginx is just an empty meta-package), instead install nginx-extras from dotdeb. this version is much faster!
• nginx.conf optimizations:

worker_processes 4; # we have 4 cores

  worker_connections 4096;
  multi_accept on; 
  access_log /var/log/nginx/access.log main buffer=16k; # log buffer (reduce slow disc writes)
  # gzip enabled
  # Cache information about frequently accessed files enabled

dotdeb packages include mod_pagespeed for nginx in wheezy

add dotdeb repos to /etc/apt/sources.list:

deb http://packages.dotdeb.org wheezy all
deb-src http://packages.dotdeb.org wheezy all

update and install nginx-extras from dotdeb:

apt-get update
apt-get install nginx-extras

create cache dir:

mkdir /var/cache/ngx_pagespeed/
chown www-data:www-data /var/cache/ngx_pagespeed/

edit /etc/nginx/sites-available/default:

server {
  #....
  
  pagespeed on;
  pagespeed RewriteLevel CoreFilters;
  pagespeed FileCachePath "/var/cache/ngx_pagespeed/";
  pagespeed EnableFilters combine_css,combine_javascript,remove_comments,collapse_whitespace;
  
  #....
}

play with the filters:

https://developers.google.com/speed/pagespeed/module/config_filters

URL-Encoding with Umlauten is a problem. Here is howto fix it:

rewrite (*UTF8)^/[öüäÖÜÄßa-zA-Z][a-zA-Z]/index.php(.*)$ /index.php$1;