I'm considering a 70-200 f/4 on a 5DII body for some portraits and events. I also want to use the lens for travel and wildlife and will need extra reach to achieve that. So I'm thinking of adding a 1.4 converter. Howver, I don't really see the use for a 100-280 f/5.6 lens at $1500. Might as well carry a cheap 70-300 lens with variable aperture. But then, why not stick to 55-200 on a crop camera. So, is 70-200 f/4 good enough with 1.4 converter?