EOS 5D Mark III + EF 50mm f/1.4 at ISO 12800 for Sports Photography?

Which is more inappropriate to use for sports photography? A 50mm f/1.4 lens or ISO 12800 or the odd combination of the two? I’ve always held the notion that given access to an arsenal of capable equipment, you exercise the right to use whatever gets the job done. I recently tested the EOS 5D Mark III with an original EF 70-200mm f/2.8 IS and shared an incredible ISO 12800 unedited photo.  Two days later I returned to the same badminton hall to catch the inter-school tournament and since I was allowed to plant myself very near the players, I was thrilled to use the 50mm f/1.4 lens instead just to give stress the camera’s AI Servo motors a bit.

With this much exposure headroom from the large aperture lens, there was really no real need to bump ISO to 12800 but I did so to reiterate a point I had already made earlier — ISO 12800 is just so clean! Nobody really shoots fast action sports at f/1.4 aperture either so doing so would seriously test the sensitivity and responsiveness of the Mark III’s Digic 5+ processor (single instead of the EOS-1D X which features Dual 5+ among other incredible technology). AI Servo on the 5D Mark III is furiously fast and I suspect the 50mm f/1.4 had difficulty catching up.

These images are post-processed. See unedited version at ISO 12800 f/1.4 1/2500 sec here

Chung Hua Middle School KB contestant Edward 50mm at ISO 12800, f/2.5, 1/1250 sec

CHMS vs CHMS: Both photographs at 50mm ISO 12800 f/2.5 1/1250 sec

Edward makes a dive to retrieve a net shot played by opponent Nicholas. A portion of the shuttlecock is captured in the frame at ISO 12800, f/1.4, 1/3200 sec. Perhaps the EOS-1D X's 14fps would be better suited :)

Another shot of Edward approaching a shot at ISO 12800, f/2, 1/1250 sec