Need suggestions on kernel settings for dedicated FreeBSD/Postgresql machine

Hi Everyone,

I manage a freeBSD server that is dedicated to postgresql.  The
machine has 4 gigs of ram and there is a single database powering a
web application that is hosted on a neighboring machine.  The web
application is mostly reading the database but there are considerable
writes and I don't want to tune the machine exclusively for writes.  I
realize more information would be needed to optimally tune the machine
but I am seeking advice on making some sane kernel settings for a
general purpose database on a dedicated system.  Currently I have:

$ cat /etc/sysctl.conf

kern.ipc.shmmax=268435456
kern.ipc.shmall=65536

and

$ cat /boot/loader.conf
kern.ipc.semmni="256"
kern.ipc.semmns="512"
kern.ipc.semmnu="256"

In postgresql.conf I have:

max_connections = 180
shared_buffers = 28MB

I would like to increase this to 256 connections and make sure the
kernel settings are giving postgresql enough breathing room without.
I suspect my settings are conservative and since the machine is
dedicated to postgresql I would like to give it more resources if they
could be used.  Any suggestions?

culley