Stacking 1.4x TCs (teleconverters) vs. 2x TC

We all know that 2x TCs provide rather degraded IQ, whereas 1.4x can look extremely good stopped down. So, I'm wondering how two high-end 1.4x TCs (Canon, Kenko pro 300 DG) will perform when compared to a similar high-end 2x TC (as above).

You'd have to combine a single Canon with an aftermarket 1.4 (or two 3rd party TCs) as two Canon TCs cannot connect without modification. Has anyone actually tried this and compared to a single 2x TC? If the quality of images is similar or better, it would be better to use two 1.4x TCs, due to the ease of switching.

Stacking 2 1.4x TCs is better in many situations as the camera can only see, at most, one TC. This affects AF operation sometimes. Yes, 2 TCs have more glass, but if you are going to be stopping down a number of stops, the IQ difference is minimal. And, for those of us with more than one body, owning 2 1.4x TCs is a lot more useful than one 2x TC.

Your longest lens (in your gear list) is the 100-400 and having used one (a good sharp example) for 5+ years I would not recommend any converters on this lens it loses too much. If you REALLY need to reach out and cannot afford the Big Guns (few can!) then look at the 400 f5.6 and crop or use 1.4 t/c. You loose versatility and IS but gain sharpness. I am afraid there are only two alternatives - LOADS of DOSH on a 600 or similar (that's what I did!) or harder, but cheaper, get closer! Getting closer will almost always give a better picture - if only I could get closer to wildlife!