Cfast cards are superior and just like CF cards and SD cards they will come down in price. The issue comes into play with the 21 raw picture buffer. With a cfast card that buffer would have been eliminated. Sure would have been nice to have that option. Its not like the 5d mark 4 is competitively priced compared to the other cameras in its class. It is at a premium price and falls short in areas that you'd think would have been addressed for a camera in the $3500 range. I am a Canon guy and have too much invested in glass to switch now. However personally I am a bit disappointed in a few things. After I rent it that opinion may change.
Use it then comment. It's an amazing camera. Shot sports no different then I usually do and haven't hit the buffer yet but I'm also not a spray and pray type of guy either. NFL... well maybe if your tracking a long play you need it but then if your shooting the NFL get the 1dx. It's basically what canon is telling you/forcing you to do.
One thing to note I got 35 frames using the lexar 1066x CF card AND this is also confirmed by TDP here: http://www.the-digital-picture.com …Canon-EOS-5D-Mark-IV.aspx
Thats 5 seconds of buffer. I got the same results.