In terms of the lens, the Nikkor Plaubel is a stop faster, but the Mamiya 80mm is significantly higher resolution.
The Nikkor is a great lens that works very well for portraits and atmospheric shots, and as long as you do moderate enlargements it performs very well.
But for really big prints (like over 1.5meters), the Mamiya will capture noticably more details.
The same can be said for pretty much any other medium format lens though. The Mamiya 7 lenses are the highest resolution of all medium format films I've seen.
Of course the biggest difference is that you can change the lenses on the Mamiya 7. I use the 65mm nearly all the time on mine.