Touring skis come in different lengths. Flotation is how stable the skis are in deep snow. Short skis can be used on groomed trails but they also can be used on terrain that has not been groomed or packed. Narrower skis are designed for performance and speed and provide less flotation. They are designed for groomed trails and packed surfaces.
Long skis are generally faster on soft snow.
The longer ski produces an easier and faster glide and spreads the load out so there is less friction between the ski and the snow's surface. On groomed trails, speed is determined more on proper base preparation and waxing. They will come in waxable or waxless varieties. Also, the use of climbing skins are an option for the waxable ski. If the temperatures in your area stay around freezing, then waxless skis may be the best.