Hardly a scientific comparison, but out of personal interest, I did a quick comparison between my 70-200 f2.8 (with and without 1.4 TC) and my 70-300 f4-5.6. All images were shot at f8, and are 100% crops (centre of image and upper, RH corner) of RAW images converted to 800x600 .jpgs. The results I have to admit are nowhere near as dramatic as I expected. (Edited to add: All Nikkor glass) 70 - 200 @ 200mm 70 - 200 @ 200mm w/ 1.4TC 70 - 200 @ 143mm w/ 1.4TC 70 - 300 @ 300mm 70 - 300 @ 200mm Thoughts? Observations?