After digesting the modern ski design thread and considering many other discussions with fellow bears I'm now at a loss to figure out why anyone would use a ski with a 70-79mm waist width.
So follow me on my logic:
1. Your boot sole is about 68mm wide. The most effective pressure transfer to your edges will happen on a ski with a similar narrow width. If you're going to just be ripping groomers then you might as well use the best tool for the job and stay on ski with a waist width in the mid to upper 60s for the fastest edge changes and the better edge hold.
2. If you're going to go hit the back side (off-piste, ungroomed, whatever you want to call it), then you should be on something at least 80mm underfoot if not a lot more. Then at least you'll get some decent float and the stability benefit in the untracked and chopped up stuff.
So the ski with a waist in the 70s is lost in my opinion. It's a ski that compromises edge quickness and hold on groomers without being really useful off the groomers. So what's the point? (and I don't think this is a GEOCENTRIC viewpoint - wink wink nod).