Would my postgresql 8.4.12 profit from doubling RAM? - Mailing list pgsql-general

Hello,

I run CentOS 6.3 server with 16 GB RAM and:
    postgresql-8.4.12-1.el6_2.x86_64
    pgbouncer-1.3.4-1.rhel6.x86_64

The modified params in postgresql.conf are:
    max_connections = 100
    shared_buffers = 4096MB

and the pgbouncer runs with:
    pool_mode = session
    server_reset_query = DISCARD ALL;

The main app is a card game with 30-500
simultaneous users for which I save some
playing stats into the db +
PHP scripts to display those stats again.

I have an option to double the RAM for EUR 180,-
but wonder if it will improve any performance and
also what to do on the PostgreSQL side once
I've doubled the RAM (like double shared_buffers?
but how do I find out if it's needed, maybe they're empty?)

Below is a typical top output, the pref.pl is my game daemon:

top - 13:40:30 up 21 days,  5:11,  1 user,  load average: 0.61, 1.14, 1.31
Tasks: 232 total,   1 running, 231 sleeping,   0 stopped,   0 zombie
Cpu0  : 14.6%us,  0.3%sy,  0.0%ni, 84.4%id,  0.3%wa,  0.0%hi,  0.3%si,  0.0%st
Cpu1  :  3.0%us,  0.0%sy,  0.0%ni, 97.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu2  :  7.3%us,  0.0%sy,  0.0%ni, 92.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu3  :  7.3%us,  0.0%sy,  0.0%ni, 92.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu4  : 10.0%us,  0.0%sy,  0.0%ni, 90.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu5  :  2.3%us,  0.0%sy,  0.0%ni, 97.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu6  :  0.0%us,  0.3%sy,  0.0%ni, 99.7%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Cpu7  :  1.7%us,  0.0%sy,  0.0%ni, 98.3%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
Mem:  16243640k total, 14091172k used,  2152468k free,   621072k buffers
Swap:  2096056k total,        0k used,  2096056k free,  8929900k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
19992 postgres  20   0 4378m 782m 775m S 11.0  4.9   2:28.58 postmaster
16184 nobody    20   0  116m  21m 3908 S  9.0  0.1  22:01.32 pref.pl
16187 postgres  20   0 4375m 502m 497m S  7.3  3.2  37:13.48 postmaster
20229 postgres  20   0 4377m 426m 420m S  6.3  2.7   0:07.01 postmaster
20201 postgres  20   0 4378m 512m 505m S  4.7  3.2   0:23.65 postmaster
20135 postgres  20   0 4378m 771m 764m S  2.7  4.9   2:14.57 postmaster
20209 postgres  20   0 4377m 571m 564m S  2.0  3.6   1:14.34 postmaster
20030 postgres  20   0 4376m 890m 883m S  1.7  5.6   3:39.64 postmaster
20171 apache    20   0  370m  30m  16m S  0.7  0.2   0:01.87 httpd
18986 apache    20   0  371m  43m  28m S  0.3  0.3   0:11.47 httpd
19523 apache    20   0  370m  32m  18m S  0.3  0.2   0:07.18 httpd
19892 apache    20   0  380m  37m  19m S  0.3  0.2   0:04.86 httpd
20129 apache    20   0  376m  37m  16m S  0.3  0.2   0:02.39 httpd
20335 root      20   0 15148 1416  996 R  0.3  0.0   0:00.13 top

Thank you
Alex