Classic tracks, what is ideal?

What is really the ideal distance between the skis in classic tracks? In Norway we have been skiing with 21 cm between the center of our skis for many years, not really thinking about why the distance is 21 cm and if we should change it. However, other people have been thinking about this, and this christmas they have tested 17 cm at Sjusjøen. See also article at langrenn.com. Christian and I went to test the tracks. Our personal test results are as follows (competetive skiing):

Normal tracks (21 cm, lower picture): Good for fast skiing; diagonal skiing, "double kick poling" and down hills.
Narrow tracks (17 cm, upper picture): Good for very steep uphills (more running, than diagonal) and double poling.

We also tested the tracks skiing very slowly. In general we think the narrow tracks are better for slow skiers, i.e. people skiing at low pace and frequency, while the broad tracks most of the time are better for competetive skiers. The best solution will probabley be to change between the two, depending on the terrain formation. I.e. For slow skiers: broad in the downhills and narrow for the rest. Competetive skiers: narrow were flat and in the very steep uphills, broad for the rest.