Originally Posted by SNPete
Make the fatter waist in the mid 80s. The thinner waist in the low 70s. For the sake of simplicity let's assume the two skis are of similar construction.
How will these two compare? Pluses and drawbacks. Why choose one over the other?
If those are the choices, pick the one that skis better on hard snow. Neither is going to be 'good' in soft snow (compared to a ski that actually IS good in soft snow) so you may as well maximize the 'good' qualities and forget the 'float' because neither is going to 'float'.
As far as qualities:
Narrow (low 70's)- quick edge to edge, easier to generate edge pressure, better on groomers, firm snow and bumps.
Wider (mid 80's)- slower edge to edge, better in spring mank, will require some bigger angles from the hips to really edge well, will ski 'all-mountain' better.
You know bikes, right?
Your question is kind of like asking: "which Freeride FS bike will be best for XC racing, a 6" travel 33lbs bike with light weight components and heavy frame/ fork or a 5.5" travel 31lbs bike with a reasonably light frame and heavier duty components?"
The correct answer is NEITHER. A freeride bike is just not an XC race bike no matter how it's configured, might as well let it be good at what it is good at. A mid-80's waist ski just can't compare to an actual fattish ski, let it be what it is. Does that make any sense?