That's not really going to be too noticeable. A ton of park skis are 90ish underfoot, so clearly it's a good width that works well.
I never notice a huge difference when go from my 79 underfoot to my 90 underfoot skis. Maybe it takes a little more to pretzel, but spinning is the same. I do notice a huge difference when I try to ride pow skis on rails. It just takes a lot more effort