I don't use superteles, and I don't know anything. But if I were you, I'd want to leverage that new 1DX with its awesome af and low noise, and thus would not consider option 3. For cases when reach is so important that you need the crop factor, I'd use the 7D, which has still more reach than the 1DIV.

Also, 1) seems a better choice than 2) if reach is what you're after.

Just my gut reaction, with the disclaimer that I'm not speaking from experience.