I own a 350d with a 75-300 lens but I am keen to shoot wildlife and think this lens may not get me close enough. I was thinking about getting either a tamron 200-500 lens or a sigma 50-500 lens. Will the difference between the 300 I have now and the 500 be really noticable or will I be spending money for little gain? Is it just a question of sitting down quietly in a strategic place and being patient with the wildlife with my current lens or will either of the other 2 let me get shots from a greater distance away? Any views would be appreciated.