srcds lag at high amount of players

[Setup1337]

Server OS: CentOS 6 64-bit
Processor: FX-4100 3.6Ghz Quad Core
RAM: 8 GB DDR3
Game(s): Team Fortress 2
Start Up Command: ./orangebox/srcds_run -console -game tf -nohltv -condebug +maxplayers 33 +ip 173.208.245.26 -port 27020 +exec "server.cfg" +map "dm_ponyville_b7" +fps_max 500
Admin Mods: Metamod, Sourcemod, EventScripts

The problem is simple. At 24+ players, the server starts to lag more and more till it becomes unbearable at 32. It causes popularity damage and the server is always less than 24 because of that.

General server CPU usage is below 50% at all times and does NOT spike when the gameserver lags. Same with RAM usage.

Server is on 100 mbit/s port. Upload and download speed history were checked and it did NOT go over 5 mbit/s at any given moment.

Gameserver rates:
66 tickrate
sv_maxcmdrate 66
sv_maxupdaterate 67

[loopyman]

Plugins? Specifically SQL plugins, logging and stats?

[Setup1337]

Server has HLstatsX:CE and Sourcebans

[loopyman]

Where is your HLX:CE sql DB hosted?
and Sourcebans.

[Setup1337]

Both are hosted on the same server as the gameservers.

[loopyman]

For sourcemod SQL plugin are you using the prefetch or threaded method?

[Setup1337]

Umm, of that I do not know. What is the quickest way to check?

[Setup1337]

bump--

[loopyman]

sourcemod/plugins/admin_sql prefetch.smx or threaded?

Or something like that. A required plugin for any sourcemod sql connections