I have not gotten my hands on the new 50-200 2.8 OM lens yet, but it seems that is the ticket for a “swiss army knife” like lens. The 300 F4 is too specialized for me as I’m not a birder and the 100-400 lenses are so similar in weight I would rather just have the OM 50-200 + 1.4x TC.
I have had the 300f4 and I now have the 150-400 and 100-400 plus I just purchased the 50-200. I have both the TCs.
So far, the 1.4TC has been attached 100% of the time when I use the 50-200. The rig is a joy to use because of the "Gandalf-like" shape and operation of the zoom and focus rings. When the rigs reach is sufficient, I would rate the IQ ahead of the 100-400 and equal or slightly inferior to the 300F4. Thus, the 100-400 is now a backup and the 50-200/1.4TC is now my wife and my walk-around lens. The rig has excellent semi-macro capabilities, and the 50 f/s makes a huge difference compared to the 100-400's 25.
Operationally, the biggest advantage to the rig I have found is, in my hand, with my left hand on the zoom ring, I can extend my index finger to the focus ring and easily move the focus ring slightly until the yellow/orange overlay indicates exact focus where I want it. (This was much harder with the 100-400)
However, when the reach is insufficient and I need to mount the 2.0TC I have insufficient data to compare IQ between it and the 100-400.
