Performance

[absolutely_free at libero.it]

Hi,

at moment I have this environment:

CentOS 
nginx + phpfpm
Dovecot, with Maildir format
Postfix
Roundcube 
MySQL backend
about 10000 mailusers
dual core Intel(R) Pentium(R) D CPU 3.00GHz
8 GB RAM
network storage device (Coraid), ext4 file system 

I have no performance issue now, but I need to move to a different  server:

FreeBSD 10.1-RELEASE
nginx + phpfpm
Dovecot
Postfix
Roundcube 
dual core Intel(R) Xeon(R) CPU            5120  @ 1.86GHz
16 GB RAM
local storage with zfs file system

My question is: is better to use SQLite instead of MySQL?
Should I prefer dbox format?

Thank you in advance for your opinion!