There is no such thing as a fast zoom. F/2.8 is slow.
Get a prime if you want real quality. Zooms are for noobs.
Really? And 2.8 is slow? Tell that to the professionals who own a Canon EF 300mm f2.8 L and who also own a 70-200mm f/2.8 L. Superb lens. I also own a 100-400mm L for travelling 'light'