You probably used the drum scanner in the graphic arts industry. There, a Dmax of 4.0 is common and desirable. At least when it comes to film used for platemaking. My densitometer can display 6.0 densities but I doubt the precision of these high density readings.
In pictorial photography, using black and white negatives, it's not necessary to build great density. Density of 1.5 is going to make white on the print. You do not need the highest Dmax.
A 100 speed film in your Zeiss Ikon Nettar will have an advantage over 400 speed film in some cases for obvious logical reasons: The finer grain. You get to take advantage of this if you use a high shutter speed, flash or a tripod. But if you walk and shoot casual snapshots in average conditions, I think a 400 speed film will really give better pictures because you will not have as much camera shake.