90% of my shots are with the 70-300L. I do have both the 400/5.6L (hand held) and the 200-400L (tripod) which are only used when I know that there will be no way for me to get any closer with the 70-300.

The new 100-400 will replace the 70-300 though I am really reluctant to let it go but reckon that 1 lens replacing 2 means less stuff to carry around. If it turns out the the 100-400 does all I want, may consider letting go of the 200-400 as well. It is heavy and I do prefer the flexibility of going hand-held. We shall see...

So question to ask yourself before dumping the 70-300L - how close do you typically get yourself? Within a 30m radius your current lens will be more than adequate for medium to large sized objects. Of course if your targets are finch sized there could be a problem getting really close.