Not here I'm afraid. My laptop is next to the router and multiboots Win 7 & 8.1 amongst other OSs.
All parameters are the same (hardware and software) except the OS. Plus, having the laptop less than half a meter from the router rules out interference. The dips are frequent and substantial. Wi-fi performance throughout my house is excellent.
My results are totally reproducible.
I still think the dips you are seeing are due to interference from outside signals. It is not related to the OS. I have a Windows 8.1 laptop which shows rock steady siganl in Inssider in one room. The same laptop when I move to the next room 20 feet away I see minor fluctuations in the signal. Another laptop in a third room at the other end of the house running Windows 7 shows occasional deep dips by about 10 db every now and then.
Even if you are right next to your router, the interfering outside signals are also there with you.