We're currently running 2 servers with RedHat ES 3.0 with the latest kernels and updates. We're running the latest Release of cPanel.
They're currently lightly used but haven't run into any problems that are limiting cPanel features or usage at all.
I've got both servers up and running with the standard installs plus:
APF - Firewall
Tripwire - IDS
Chkrootkit - Root kit checking
MailScanner
Spamassassin with DCC, PyZor and Razor
Logcheck
Mrtg