Activate and Change Product Key should have the same effect.
Microsoft's official policy is that you can not use a new OEM Windows 7 license on a PC you are building for yourself. You have to use a retail copy. If you ignore this policy Microsoft has the right to permanently deactivate that license.
Also, I do believe, if I continue with OEM, if I ever upgrade my motherboards, I might have a hard time getting a new activation key from ms?
If you replace the Motherboard on a computer you purchased, you can attempt to activate by phone. You will eventually get transferred to a real person (I think you can continuously press 0 to get transferred faster). When you do, explain the problem and if the person is reasonable they'll give you a new activation code.
So, upgrade to windows7 home premium family pack retail, clone, delete "upgrade" from registry on cloned drive, sysprep, install in other computer, change product key, use new key provided with fam pack. Does this sound like it would work? Thanks