well i am really impressed with my 1.4Tc on the 300f4L at 420mm 5.6 on the 5Dmk2 its quite goodNot so - with the same framing the 22mp will always look better than 18mp.Squibby, please. It's unfair to say "well my FF with a lens that costs $7000 more than your lens does better than your crop."
FF shooters are clever enough to have the extra reach lens. So 250mm on a 1.6 would be matched against a 400 on a ff. I know which image will have the best IQ.
Put that same 400 on the crop and shoot a subject 100 yards away and we'll see who wins.
I'm curious to see how the 5D3 with a 1.4 extender compares to a 7D without. The extender loses you a stop of light, but that's made up for by the much better ISO performance. The main problem is that you can't put that extender on an f/5.6 lens (or the 100-400mm).
Of course the 5D3 + 1.4 = almost $4000, which is about what I paid for my refurbished 1D4.
i'll get some pics i took with it (note i am not a bird shooting fanatic so the pictures i post may be rubbish by everyone elses standards