It's magic for four shades do to the curve design and the long back slopes really helps - but it's not 6 or 7 shades. For us - 4 shades is minimum. The 3 shades of ABW does not cut it.
What you give up in absolute supreme fidelity you gain in absolute supreme flexibility. You won't see it probably until you get out a loop. We will be able to resolve more detail in K6/K7 if you giving it very high optical resolution scans. For example - if you are drum scanning large format film at 4000dpi - K7 will absolutely kill it with detail you never imagined possible in 30x40 prints. And that was the norm in the beginning - way back in the early 2000s - nearly everyone using it was drum scanning large film. Digital cameras were pretty low res at that point and drum scanners were everywhere...
Still we have a Hell 3400 drum scanner in our studio and still our scanning clients will not settle for less on there 2.25 or 8x10 film.
We may put out some paid for samples for comparison with the same file on a K6 and a K4.
When you begin to blend the inks together - then it really begins to look like more than a quad set.
Hope this explains.