@sudorandom : sorry mate, I  though your question was regarding automatic reboot and CCI state while upgrade.
For network upgrade no reboot is required, but there is a few minutes of network downtime during the upgrade of ports.
I didn't find it documented anywhere, however there is a disclaimer on customer portal that that states, "Your virtual server will be automatically rebooted for upgrades to CPU cores, ram, and disks."[1]
It doesnt mention port speed upgrade

[1] https://manage.softlayer.com/Sales/upgradeInstanceRequest