« on: May 19, 2013, 04:31:50 AM »
From everything you write the 70-300L is your lens because it unifies a small pack size (veeeery important when outdoors) with good iq (sharpness wide open, boekeh) and "always on" reach. For prolonged use it's important the weight is way below the 70-200L/2.8, and the 70-300L feels even less heavy because it's shorter, i.e. putting less torsion on the wrist.+1
When outdoors using a tc often is a pita since it takes time and it lets dust/sand enter the camera, but a Kenko tc (Canon doesn't fit) works fine with the 70-300L though the af performance/precision degrades somewhat, ymmv.
Besides that, what you need to do is to see the focal lengths you shoot at. That should tell you what you need. I got the 100-400L for birds and animals. Having said that, I shot with it at the Grand Canyon and I did use it at 400mm.