Make custom mtu setting permsnent

[Dave Feustel]

I want to make a custom mtu setting permanent so I don't
have to reset it each time I boot. I've found three files
where I might be able set the mtu for eth0:

/etc/sysconfig/networking/profiles/default/ifcfg-eth0
/etc/sysconfig/networking/devices/ifcfg-eth0
/etc/sysconfig/network-scripts/ifcfg-eth0

To which of these files should I add the custom mtu setting,
and do I simply add 'mtu 7200' on a line by itself?

Thanks.