I will be checking a few EOS lenses of a friend of mine soon. None involve an ultrawide.
At some point, I can always try the C-V 12/5.6 once I fit it properly. This is the same lens that was also made in a Nikon F mount (but needed the mirror lock up to use).
Frankly, i am not that interested in checking how each lens does without the SB optics. Most of the lenses I have, I already know. From what I see, the SB optics, not only increase the aperture but also the sharpness and the contrast. The ones I show from the EF 50/1.8, in the post, I had to tone down the contrast. This is seldom experienced with an f/1.3 lens, wide open or even with an f/1.8 wide open, even more so in diffuse/poor light.