The eagle owl is a large owl. Let's now do the same experiment with one of the smallest, the Tawny Owl* and see the difference. Again, I've counted the frames in the top right corner, Up frames are in red and down frames are in green.
up 4 4 3 4 = adv 3.75
down 4 4 4 4 = adv 4
We can see that there is a difference from the large bird to the small bird. Obviously the small bird's flight cycle is faster, also the cycle is much more even in terms of timing. Although, on average the wing still takes longer to rotate down than it does up, and at no point does it move down faster than it does up.
The same again with a medium bird, a barn owl.*
up 5 5 4 5 5 5 = adv 4.83
down 6 7 7 7 7 8 6 = adv 6.857
As we might expect the medium sized owl is in the middle of the previous birds, both in terms of speed of cycle and the ratio of frames up to down.
We can now use this knowledge in creating our flight cycle. The movies were shot at 50 frames per seconds so by halving the time of their wing beats we get a rough guide to the speed of our cycle, and we can use the following ratios for flight cycles of owls of similar sizes
large = 1/1.7788