Are the TC IIIs really better on lenses other than super tells?

I posted this in the TC thread and got no response, so starting a new thread. Presently I have version II of the 1.4x and 2x Canon TCs. I recently upgraded to the 70-200 II. I have seen completely conflicting reports on whether I should upgrade to the III TCs to get acceptable quality with the 70-200 II when extended. Some reviews say the benefits of the III TCs are only visible in the new Super Telephoto II lenses. Some reviews say there are night and day differences even with a 70-200 and so absolutely upgrade from II to III TCs. Having spent a lot to get quality lenses and body, I am certainly willing to spend another couple hundred bucks to get the III TCs, but would rather not if there will be near zero effect on the output. Any concrete conclusion on this based on experience here?

As a side note, my goal here is to avoid adding a 100-400 to the bag, and I do understand the AF speed I give up vs. the 100-400.

Title should be "Superteles", not super tells... darn spellchecker!

Reviews suggest the III of the 2x TC is better, not so much with the 1.4 TC.

rick_reno wrote in post #15297234
Reviews suggest the III of the 2x TC is better, not so much with the 1.4 TC.

This, really.

If I had a mkII 1.4 I wouldnt upgrade unless I had the new supertele.

The mk III 2.0 is enough better optically to go for it.

I recently upgraded from the 2x II to 2x III. On the 300f2.8, the 2x III clearly offers better contrast and slightly sharper in real life shootings of California condors in difficult lighting conditions. When used with the 500f4 II, the image at 1000mm is still excellent (search my name for a post of a peregrine falcon and a coyote with the 500f4 ii and 1.4x II and 2x III). Based upon other reviews, I have not bothered to upgrade the 1.4x II yet. The quality and AF performance of the 1.4x II with either the 300f2.8 or 500f4 II is fantastic, so I'm not sure if I would see any difference.