If you only use the 300mm range every once and a while, and you're willing to accept lower image quality when you do, then the 70-200 f/2.8 IS is a great alternative to the 300mm f/4 IS. Sounds like the best choice for you. But most wildlife shooters need more range, even on a crop camera, so the 100-400 f/4.5-5.6 is an excellent alternative. Good luck.