I once bought a CV 50/3.5, supposed to be "one of the sharpest 50mm's ever", and returned it after a week and two rolls of Kodak Ektar 100 side by side compared with the Canon 50/1.4.
I found that the peak resolution of the collapsible Cron (screwmount) is a little bit higher yet as the Canon, but overall contrast, shadow details and backlight behavior of the Canon are much better!
It's my sharpest 50mm screwmount lens by far. I doubt that anyone who have it will feel in need of a CV Nokton 50/1.5.
IMHO only one thing can be said against the Canon 50/1.4, that the rendering is more on the "cold" side and it's "too sharp" or "too modern" in outcome. So that's why a 50/1.5 is a great addition to it.