FF back to crop. Anyone made this journey?

I can't go back to crop.

I bought an EOS M last year and I hate the image quality so I will eventually replace it with an A7 or future Canon equivalent.

David Arbogast wrote in post #16714919
I preferred the image quality result using extenders with the 5D III + 500mm f/4 to compensate for crop factor. For instance same subject and same setting: 5d iii + 500mm + 2x vs 7d + 500mm + 1.4x, I preferred the 5d iii image. However, AF gets more limited on the 5d iii in that scenario as the 500mm + 2x is an f/8 lens assembly.

I only speak in terms of personal preference, I respect differing opinions.

This makes sense. And a comparison at TDP confirms your tests. However, the results are very close and with certain combinations, the crop will be a much cheaper option. I do have a 2x TC and will probably keep it as 200mm is my longest lens and I don't need to get to 400mm very often.

For me, even though I don't mind big and heavy equipment, I am interested in getting a cheap, 'disposable' crop kit that I won't mind breaking or losing. I have had a 5D with the 24-85mm & 70-300mm IS lenses for this purpose (which would be the equivalent of the 18-55mm and 55-250mm crop lenses) but don't like the lack of IS on the standard zoom nor the AF or IQ on the telephoto zoom. And the 5D doesn't do video.

I would like to get my hands on the two STM versions of the crop kit lenses, but not sure which body to get. I've got the M, which I love despite a few quirks, but it doesn't have a native telephoto zoom. I'd hate to buy the adapter for just the one lens (55-250mm STM). I'm thinking of trading it in for the SL1 now that the price has dropped.