I didn't think TC on the 400 would be a good way to go, but you never know...always have to ask. I have the 7D also and was thinking that the 300 would be the way to go, but thought I would check. I have that 70-300 and I like the distance that gives me, but always wondered about having another 100 to the end. I am going to give renting a shot and see what comes of it. Thanks guys for the input.
Jayson