This isn't quite what you trying to learn but it's from a similar quest. A few years ago I got a very good deal on a D7100 & thought that it with 300 mm might have more left after cropping than my 1D4 at 400 mm. The primary idea was to reduce the load I shoot with at the R/C events. The Nikon was shot using their 28-300 which I would have need as my flight lens so that's the lens I used in the tests even though I had their 70-300 VR G which was a sharp copy. When the 7D2 came out I sold off the Nikon gear because it didn't meet my needs. There just wasn't a good enough superzoom for the nikon to replace my 28-300 L IS on the flight line nor a xx-400 to match my 100-400 L IS. I can say that the 100-400 didn't see any use this year after getting the Sigma 150-600 C which has proven itself to be up to my needs even though it's a bit on the heavy side.