70-200f/4 IS L + 1.4tc or 70-300 f/4-5.6 IS L?

Which of these would give the best IQ on the long end? How does the 70-300 compare to the 70-200 at 200? As the 70-200 with the tc would be f/5.6, are there any obvious disadvantages to choosing the 70-300 over the 70-200? Size/weight not an issue. Any observations welcome.

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lee uk.
There are old pilots, & there are bold pilots, but there are no old bold pilots.