Hi, I currently use a 50d camera with a 70-300mm canon lens and would like to upgrade this lens and have been thinking of the 100-400mm lens. But recently a 300mm lens has become available at a good price so am not sure whether I should get a prime lens with a 1.4 teleconverter. I like the versatility that the 100-400 has, but hear that at 400mm it is soft. I will be using this lens many for wildlife work. Your recommendations would be appreciated.