Well I am staring to look at adding another lens to my bag and initally was set on the 70-200 f4L IS. That is until I saw the 70-300 f4-5.6L IS. Can someone tell be the real world pros/cons between the two. I like the 300 for the longer focal range and is not too much more in price so I was thinking it would be worth getting over the 200. Where will I see a real difference besides the obvious focal length. Thoughts?