I would imagine that the standard settings are the optimal on average. It's impossible to say beyond the default settings as it will be indivdual to each and every server. Have a play and settle on what works for you. Alternatively, don't use the spamd approach
my $cpspamdconf = "/etc/cpspamd.conf";
my $spamdoptions = "";
my $allowedips = "--allowed-ips=127.0.0.1";
my $maxconnperchild = "";
my $maxchildren = "--max-children=5";
my $pidfile = "--pidfile=/var/run/spamd.pid";
my $localonly = "";
my $timeouttcp = "";
my $timeoutchild = "";
No idea. You really do need to do some work yourself rather than having everyone else do it for you . Go have a look over on: http://www.spamassassin.org
As chirpy stated, each server is different, the standard (default) settings would be the start but each and every server needs to be "optimized" individually as what would be ideal for one may not be for the other.