Interesting because I use the lens very often. I was lucky to buy an almost new 67II, 165mm and 75mm as a set on the second hand market in the Netherlands for an exceptional low price. All items in new condition.
I am very impressed by the performance of the 75mm but would hesitate to use f4. To my understanding (Pentax 6x7) medium format lenses in general show optimal performance from f8 to f11? Is this lens in your opinion an exception? Are there any test reports available?

Jos.