OP, you obviously came here looking for advice, so I would suggest you take note of the suggestions already posted as to why you should re-install windows for a new mobo...
CPU's, chipsets, bios versions/functionality, north/southbridges, hardware-specific drivers..etc etc....they all change regularly. Sometimes the changes are minimal, other times they are quite significant....all of which could cause major issues with an older Windows install that is bloated & full of old registry keys, outdated kexts etc etc...
If this happens you will spend way more time attempting to pinpoint & correct the issues than you will if have to reinstall windows & some data/files....