I am thinking about trading my 24-105 f4 L, the original version for a pristine Canon 2xIII TC plus $125.
I have a 24-70 f2.8 and I use it far more than the 24-105 but not sure I want to ditch the handy focal length of the 24-105.
However, the last time I used the 24-105 was in 2015 for a trip to Yellowstone and Grand Teton, it is a sharp copy.
I paired the 2x III with the 100-400 II yesterday and did some manual focus shots out the window of my truck at the local duck ponds and got some very nice images. Very sharp. Nice to have a little more reach.
I already have the 1.4xIII and use it quite often with the 100-400 II.