[RCU] Question about Roundcube memory usage and max mysql threads

Hello

This is my setup

• 1 Quad Core Nehalem @ 2.80 ghz
• 12 GB of ram
• RAID 1+0 of 8 SAS 15K rpm disks
• Red Hat Enterprise Linux 5.6 x64
• Apache 2.2.3, PHP 5.3.6, Mysql 5.5, php-apc
• Latest stable roundcube version (0.5.2 today..)
• IMAP server: dovecot 2.0.11 in another host

I must support 1.200 concurrent users with roundcube (we are almost 15.000, 10% of concurrency is not a bad deal), and I have the following questions:

• How much memory does roundcube uses?
• How many mysql threads should I use for 1.200 concurrent users?
• Any performance hint about this setup?

Regards

Maria