I have the same camera. If I could use only one film, I would take the 400. By the way the shutter does go up to 1/700 at f/11 and smaller. Since you only get 15 or 16 shots a roll depending on whether you have a later or earlier model, you could just bring a variety of films since you might have to change rolls often anyway. But the range of speeds and apertures on the Fuji will cover the brightest light you will ever encounter even with ISO 400. Worst case scenario would be 1/400th at f/22, which is sunny 16 minus one stop for snow. Mother Nature does not get brighter than that.