Aperture 1.2 @ISO 100 and sunlight anyone?
Assuming Sunny 16, 1.2 and ISO 100 should result in a shutter speed of 1/16000, if my calculations aren't completely off-base. And that's just a rule of thumb, it could be brighter.
I only had one time where my cams maximum of 1/4000 wasnt enough. that was sunny and f1.8 iso 100. In that moment i wished for faster shutter speed. But it never happened again so far
Now i really dont know what the 1/8000 shutter is needed for. Sports perhaps to freeze the action but i think for sports one uses tele lenses and they arent super wide open so they dont need 1/8000 also. And often some kind of "action blur" is not bad but enhances the image.
Just checked the hummingbird and saw many photos with 1/4000 and u could see the birds wings clearly.