But the 70D may well be better than the 6D at focusing on things that move, even something as slow as cricket.... I'll leave it to others to comment on that, as I don't photograph that sort of thing. It could be that the two factors you singled out - low light performance and shooting action - lead to conflicting recommendations (the 5DIII will give you both, but at quite a price), so you'll have to decide which of the two matters more. Any chance of renting in your part of the world so you can find out first hand?
While it would bore everyone to death if I replied to everyone I had to pick up on this too . . . cricket? Slow? You might not know it but AI Focus was actually invented specifically for cricket. You focus on the cricketer and in case something unexpected happens and he actually moves (heaven forbid) you still get the picture!
It's actually (like so many things when you really analyse them) a really interesting subject. With the players wearing all white (traditionally at least) you need to be careful on exposure and the action which can actually be quite brutally fast when it does happen keeps you on your toes. The challenge of getting both the batsman hitting the ball and a fielder catching it as well a second or two later can be quite entertaining as it's so unpredictable!
Oh, I know, I know; you weren't supposed to take my comment seriously. I grew up in Australia and England and was forced to play it (and rugby) at school. As a cricket-hating schoolmate of mine described it, hours of boredom interrupted by moments of terror. Or as Robert Morley once described it on "Any Questions" in the mid 1970s - "an awful, boring game played by awful, boring people and watched by awful, boring people." But yes, it can't be easy to photograph....