memory consumption of php5+fastcgi

[ispcomm]

I'm wondering what the memory requirements would be for a real server hosting domains with ispcp.

Using fastcgi+php5 (debian etch, default install) each php5 process is using 5900KB of memory (that is... almost 6megabytes).
Every site has 3 stand-by processes.

Allocating 100 domains (as a minimum requirement per physical server) would mean that 100x3x6 = 1800MB or RAM would be needed just to host the idle processes for all domains. This is on a 32bit machine (64 bit could be double this numbers).

If you add a few connections and the other daemons (primarily mysql) you'll end up with a minimum requirement of 4Gbytes that is too much IMHO.

My fear is that adding other stuff to php would get this number higher (currently my php5 has only the gd, idn, mcrypt, mhash and mysql extentions).

My question is: is there a way to reduce this number, other than reducing the number of idle processes that fastcgi spans ?