Float and downhill performance tbh - the Nansens are a great trail ski but get off trail in Colorado winter snow pack and you aren't going anywhere.
I don't know how much you weigh- but my personal experience and testing is that I do not generally notice any difference in flotation between my 54mm-waisted E99s and 60-62mm-widthed skis (e.g. Eon/E109).
However- width is not the only dimension that affects flotation- flex matters as much:
-my 210cm Combat Natos (62mm) offer just as much flotation as my 195cm Annums (78mm)- due to the flex offering full-length stability in deep snow (though the rounder flex of the Annum makes them easier to turn).
-my 210cm Combat Nato (62mm) offers MUCH better flotation than the wider 195cm Epoch (68mm)- again due to flex (though the rounder flex of the Epoch makes them easier to turn).
-my 205cm Eons and E109s are absolutely useless in truly deep snow as their flex is completely unstable- they are both actually worse in truly deep snow than the narrower E99!
-my 188cm Storetind (68mm) (FT68) offers as much flotation and stability as both the 210cm Combat Nato(62mm) or the 195cm Annum (78mm) (and the ST offers MUCH better downhill performance than the Annum- sidecut, tip rocker, and torsional rigidity (the Annum is a wet noodle under pressure)).
Bob's description of the flotation of the FT62 suggests that its very stable flex supports more flotation than its meager 62mm waist would suggest...This would suggest that the FT62 could offer more float than the 56mm Nansen...
However- the Nansen is available in traditional XC lengths as well...If the Nansen has a stable flex, I doubt that a 188cm FT62 offers any more flotation than a 205cm Nansen...
How would you describe the flex of the Nansen?
Now- this has to be taken with a grain of salt as always- that grain of salt is CLIMATE.
I must be clear that I get a LOT of snowfall in my local climate- BUT, the majority of that snow is heavy and moisture-rich, and many of the heavy-snowfall storms are associated with high winds. My "deep" snow does not match the profile of true "champaign" powder snow that one gets in the western dry mountains. Even when I do get that bottomless dry powder it rarely lasts more than a couple of days, before it consolidates.
So- my point is that- due to supportive flex- my 68mm Storetind (FT68) offers even more effective flotation than my 78mm Annums- and, as such it is really the most flotation that I need in my local climate- even in 130cm of fresh snow (which is what we got last week!) I cannot speak to whether the ST/FT68 would be enough flotation for that deep dry pow you get!
I should also point out that when I do get that bottomless dry powders snow, my 210cm Combat Natos actually are more stable and supportive than the very soft round-flexing Annum...
I also have an AT setup but it feels like overkill for the terrain I'd like to be skiing. For skiing up and down mountains it's great but all winter the avalanche danger is too high for that so I'm limited to low angle skiing anyway.
I "toured" on an AT setup alot in the late 90s- for up and down it cannot be beaten- but I freakin hate it
for any touring that involves significant horizontal distance- I need ye-old Nordic metatarsal flex!!!!