I have not used the 50 or the 80 but I do use the CZJ Sonnar 180mm 2.8 on my Pentax 645Nii with an adaptor and I absolutely love it. Based on a few non-scientific comparison photos between my SMC Pentax A 645 150mm f3.5 and the CZJ 180mm 2.8 Sonnar the 180mm wins in image quality while the 150mm wins in ease of use. The CZJ 180 is one huge chunk of glass and metal. It is the only lens I use on my 645Nii where I am glad that there is a tripod mount on the lens. On the flip side, the A 150mm is a very nice, tidy little lens and is very easy to pack around and use. If I am hiking then I will definitely pick the A 150.

Here are a couple similar shots. Both shots taken with the Pentax 645Nii within about an hour of each other, similar light. Tripod mounted, manual focus. Used Kodak Portra 400VC set to F6.7 @ 1/1000 seconds. No shutter release cable, no timer, no mirror lockup. Developed in same batch with Rollei kit at standard timings.

SMC Pentax A 45 150mm
Pent 150 Flowers.jpg

Carl Zeiss Jena 180mm Sonnar
CZJ Flowers.jpg

They are very close. To me the Pentax image seems a bit warmer while the CZJ image is a bit cooler. I think the CZJ image is a tad sharper but I am a long way from an expert on this. You should also keep in mind that individual copies of the same lens can vary a bit so this result may not necessarily be representative of anyone else's experience.