Slow performance after falling back to MySQL 3

[Rainer]

Hi folks,

Yesterday I have upgraded my linux box with a pair of Xeon 1G CPU and
reinstalled everything (it was a sinle Xeon 700). The default RH9
installation comes with MySQL 3.23.54. After the reinstallation I
found the machine was not as responsive as before. (It's not very
slow, but some lagging is noticed)

I was running Mysql-max 4.0.11 and the performance was ok, except the
slowness during the peak hours, which was regarded as normal. I would
like to know the differences between Mysql 3 and 4. Is the new version
making a significant jump in performance?

I also noticed the system eats up memory faster than before. With the
old setting the system never used up 60% of physical memory, even at
extremely high loading (30+). Now it easily used up 70% of memory.

The server is running Mysql only. It's equipped with 2 Xeon 1G and 2G
of memory. The kernel version is 2.4.20-8smp #1 SMP. Also attached the
my.cnf for a clearer picture:

mysqld]
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
skip-locking
set-variable = key_buffer=384M (it was 512M)
set-variable = max_allowed_pac ket=1M
set-variable = table_cache=512
set-variable = sort_buffer=4M
set-variable = join_buffer=2M
set-variable = record_buffer=4 M
set-variable = thread_cache=25 6
set-variable = max_connections =400
set-variable = tmp_table_size= 64M
set-variable = thread_concurre ncy=4
set-variable = myisam_sort_buf fer_size=256M
#log-bin
skip-innodb

[mysql.server]
user=mysql
basedir=/var/lib

[safe_mysqld]
err-log=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

[mysqldump]
quick
set-variable = max_allowed_pac ket=16M

[mysql]
no-auto-rehash
# Remove the next comment character if you are not familiar with SQL
#safe-updates

[isamchk]
set-variable = key_buffer=256M
set-variable = sort_buffer=124 M
set-variable = read_buffer=2M
set-variable = write_buffer=2M

[myisamchk]
set-variable = key_buffer=256M
set-variable = sort_buffer=256 M
set-variable = read_buffer=8M
set-variable = write_buffer=4M

[mysqlhotcopy]
interactive-timeout

I'm not expert in system administration and need advices badly from
you guys. If the recommendation goes to upgrade, which build of MySQL
4 should I choose? Thanks a lot in advance. Sorry for my poor English
as my mother tongue is not English.

Cheers,
Rainer