Depends. An 81A is useful under blue overcast skies, although Provia is fairly forgiving by itself under such conditions. You just have to judge the
processed chromes over a lightbox to see if you like the effect better with or without the filter. On the other hand, a skylight filter is really better for
cutting UV at high altitiude, which can slightly affect image sharpness over long distances. While I prefer a 1B for Velvia, these newer multicoated
"colorless" UV filters seemed to work better with Provia for that purpose. Fuji chrome film is fairly forgiving at high altitude, but there are minor
improvements which can be made with filtration. And I have done one heck of lot of high altitude color photography, mostly large format, though
every format seems to be getting one size bigger as I get older. That's because gravity is a function both of altitude and time. The further time progresses, the heavier your pack weighs. Isn't that Einstein's Second Theory of Obnoxious Relativity? It's all relative to your age.