Hi. I cannot speak about use of the Hassey primes after buying the zooms. However, with regard to the UV filter choice, I have a firm view that others may not fully agree with.
Why spend (ok, no other lens choices available on the Hassey) such an investment in a system and sensational optics only to add second rate glass to the front? Think about it - what passes through the first piece of glass has an impact on what the next optics in the chain will receive. I just would not dream of adding any poor quality uv filter to any of my Hassey or other lenses. Yes the options are limited and pricey, but it is only logical.
Yes, the difference noticed my very often be litte or none depending on what you shoot and how etc.. But at that critical time it will. The issue is much the same for the whole Hassey/Zeiss system you invested in - is it always different to say a Bronica SQA? Probably not.
Last week, I saw a guy buy a $4k Nikon DSLR and a $3k top end lens and when asked what UV he wanted - he said "the cheapest possible" !
Hoya makes good stuff but there are categories. I use the double sided multi-coated pro version. To keep the cost down (as we all want to do), I just negotiate harder rather than buy consumer versions. I also hunted around for very good used Hassey versions - KEH has them occasionally.
Finally, I suggest you avoid the trap of thinking of the uv as only a protector that may get broken anyway. It is more than a protector - yes if it gets damaged that is better than damaging the Zeiss front element or more, but the uv's role and affect is more significant.
