Let's combine all speeding up tricks for silverstripe and websites generaly.
Mine:
memcached for sessions,
client side swf image resizing,
turned off mod_rewrite (just set 404 page to sapphire/main.php it's faster),
imagemagic server side image resizing,
wget retriving remote data,
xcache,
analytics js-scripts sometimes is slow so server side analytics,
minifing of HTML, JS, CSS,
caching of everything that isn't changed,
expire headers,
subdomain for static content and ngix running on it (CDN and dedicated IP will be better),
gzip compression,
removing dev servers directive,
combining css and js as much as possible