Never had to reactivate in a situation like yours, but based upon the questions of other members, the new MOBO, will require a call.
But it is not a problem, I have seen at least a dozen posts asking about the reactivation call; each poster showing concern. The result in every situation was that they were reactivated and they commented on the professional, polite attitude of the Rep. Remember, MS, has to do this, to protect their invesment in R&D, but they, also, know, if they give you a hard time with the reactivation, customers will be reluctant to use Windows in the future.
Just one little hint. When asked for your key, do not give it. In fact make sure the box allowing automatic activation is not checked. After you are installed and have your programs and everything, just the way you want it, activate at that point. After activation, make a system image. You will never need to activate, again. You have 30 days to activate after install.
If you insert your key number when first asked and you do not like the install, you have to install with the key, again. Even though the Rep will be cooperative, after a number of calls they will start to ask questions. They will require more than 3 (some say 6) before trouble begins, but why ask for trouble
Enjoy your new rig, sounds really nice.
EDIt: Jonathan Real nice phone listing.