I can't speak for the Zoom but the 45mm is absolutely outstanding. Edge to edge, corner to corner sharp. The only other lens I own in that focal length range that is as good or better is my Schneider 60XL.
Victor
I know this is not a direct comparison at 45mm but I own both. In fact the truth is I could probably just use the 32-64 for pretty much everything. But... my, oh my... each time I use the 45mm the colouration and look of the photographs is just drop dead gorgeous (to my eyes, at least).
This is probably the most interesting use of the 45mm last year - shot from the top of the BT Tower in London on a rare occasion it was open to the public (by ballot, only). Shot through glass (of course) and without a tripod. I've linked through to the a very large size of the photo.
In several situations where weight and size have been critical, the GFX50S plus the 45mm is so compact and even - dare I say it - light that it has saved the day.
Like hiking over the top of a high moor in Yorkshire in the snow:
There is no easy answer to the dilemma of which one. If there was I'd only own one!
If I had to choose only one, I would go with the 32-64 because it is more versatile but until I really do need to release the capital tied up in the 45/2.8 I am keeping it (and hoping I never have to sell it to fund my lens lust).
Incidentally, I do own a better lens that 45mm - the 23mm f4 which is just about the best of any lens from Leica, Nikon, Zeiss, Voigtlander or others that I have ever owned.
LouisB