So the 1DX is doing 12fps at 18MP.
That's 216MP/second, with dual DIGIC V.
If the 5D3 is only a single DIGIC V (just as the current 5D2 is only single chip, then that's 108MP/second.
At 22MP, that's just under 5fps.
If the 14fps (JPEG only) figure is used, that's about 5.7fps with a single DIGIC V.
The 5D3 will not do 6fps.
Thats also assuming the camera doesn't chew up extra chip speed for intermittent AF in burst modes and metering (the 7d and 1dx had a separate chip just for AF)... So we could then be back down to 4fps
I could be happy with 1fps if it meant that the auto-focus was 100% right 100% of the time.