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Thanks for posting the above comparison images. Even though I own the Zeiss 135/2 lens, after studying the images you posted, I have to admit that overall I do find that I prefer the Plena image.
You said that the Plena has "lack of vignetting and clarity of the whole frame." I really didn't notice any vignetting in the Zeiss image; nor did the Zeiss image lack clarity of the whole frame. To my eye, I preferred the Plena image because I thought it had the better looking background blur, AND I preferred how the Plena rendered the subject (sharper, more 3D like pop, better contrast).
I'd certainly trade my Zeiss 135 lens in a heartbeat for the Plena.