8.2 slower than 8.1?

About 2 years ago, I ran some benchmarks on a Compaq DL380G2 I use for
Postgres[1]. I tested a variety of disk configurations to compare
setups. I'm rebuilding the machine now with upgraded hardware and I'm
dumbfounded by substantially slower performance. Here are the specs:

Compaq DL380G2, 2x1.44ghz, six internal disks with Smart Array 5i
controller.

Prior Now
-------------------------------------------------------------------
OS CentOS 4.2 CentOS 5.0
Filesystem ext3 ext3
postgresql.conf Stock Stock
Ram 1 GB 3 GB
Postgres 8.1.2 8.2.5
Smart Array 5i (builtin, 16mb) 5302 (128mb cache)
Drive Config 2 disk RAID-1 (os/log) 2 disk RAID-1 (os)
4 disk RAID-10 (data) 4 disk RAID-10 (log)
14 disks RAID-10 (data)

I'm using the six internal disks as a 2-disk raid-1 mirror for the OS
and 4-disk raid-10 for the log on the internal 5i controller. I have an
external 14-disk raid-10 connected to a Smart Array 5302 (with 128gb
cache in a 75%/25% read/write setup).

I ran my benchmark script again (see below) and the performance dropped
60% at 1 and 2 users and 27% and 17% at 5 and 10 users respectively.

Any ideas what might lead to this decrease across the board?

Brian

[1] http://www.ghidinelli.com/2006/01/17/postgres-812-benchmarks/

Here is my simple script:

#!/bin/sh
# pgb.sh
HOST=localhost
USER=postgres
DB=testdb
totxacts=1000
for c in 1 2 5 10
do
echo "Starting test for $c users..." 1>&2
echo "== $c concurrent users, 500 transactions =============="
dropdb testdb -U $USER
createdb testdb -U $USER
echo "Initializing benchmark database"
pgbench -i -U $USER -s 10 testdb &> /dev/null
echo "===== sync ======"
sync;sync;sync;sleep 10
pgbench -n -U $USER -t 500 -h $HOST -c $c $DB 2>&1
done