The 80/5.6 El Nikkor is a much better corrected lens. The 80/4 was a budget version with one less element, less than ideal corner MTF with MF film, and a slight focus shift from wide open to one stop
down. But for 35mm it's a very nice bargain - brighter initial focus, and quite sharp with good internal
contrast when using just the center of the lens. Plus I picked one up a virtually new one for next to nothing. In MF don't shoot 6x6 but 6x7 and 6x9; so a 105 would be the traditional "normal" for that,
though I personally prefer to use a 150 Apo Rodagon N - again using just the center of the lens. It's
a "wow" lens, and they also made a 105 in that series. I once owned a 105 Componon S. It was quite
good, but certainly not in the league of the expensive Apo Rodagons.