I have the Panasonic 14-42 kit zoom lens. Zoomed out to 14mm, it can be opened up to f/3.5. What benefit would the Oly 17mm f/2.8 give over the 14-42 lens set up as above? Is the only real benefit that it's a smaller/lighter lens? For a 35mm equivalent lens, should I go with a faster lens (e.g., < f/2.0) to see an appreciable difference vs what the kit zoom lens can produce?