I've shot with the Mark II's and Mark III's but Zeiss' Super Speeds are something special in general. But Matt Duclos of Duclos Lenses says it best:
"The update to the B-speeds included an all new mechanical design for the entire set. While the optics remained the same for the 18mm, 25mm, and 35mm, Zeiss refreshed the optical design of the 50mm and 85mm. The Mk I lenses were released in the mid 80’s. It was at this point that the Zeiss primes began to shape the motion picture prime lens design for decades to come. The Mk I primes all had a common 80mm front diameter, integrated focus gears, and sported Arri’s brand new “positive lock” PL mount. While the focus ring gained a very useful 32-pitch gear, the iris remained a knurled grip that, at first glance, can often be confused for a low profile gear. After-market iris gears can be added to the Mk I primes to modernize them a bit more, but beyond that, they don’t need much help."