>> I tried the installing fast-cgi on a very busy expression engine blog installation (100,000+ hits/day) and I would end up with
>> way too many cgi

The usual setups with nginx+php involve static number of spawned php processes (I haven't seen any usefull adaptive spawning case).
You can use the 'spawn-fcgi' (which came with lighthttpd and afaik is now also a seperate project) or my choice would be to use
php-fpm http://php-fpm.org

rr