I think PSB may have the TRUTH here
. While the Borrani's may bend at the spider when stressed beyond the limits of old 155/165 x 15 Pirelli's, say with CN36's or even more adhesive rubber, the Fergat's BROKE!!
Maybe that's why I collect the Borrani's?
Most of my experience with these wheels on the track was 40+ years ago with much less adhesive rubber. I never broke a Fergat as everyone used the Borrani's. They probably knew something even back then.
Just my opinion.
Gordon Raymond