I don't think there is a best practice for that. Especially since we don't know how long they would be in stock and if there would be additional updates in the mean time.
I think the best thing would be to leave them at current version and upgrade at the time of deployment. There is a pretty easy over the web upgrade option on Unleashed now. Just set it up via the wizard and when you first log in go to Admin & Services -> Administer -> Upgrade. Choose the Online Upgrade method, select the firmware version and click Upgrade.