On the low end of "b" for me. I try to hold out for stationary animals, but I actually have a pretty good record on running critters. I honed my technique on running coyotes during my formative years.
The only miss on big game that I can remember in the last twenty years or so was a kudu running flat out in Namibia--shot just in front of him and there was no second chance. I made up for it later by shooting a duiker juking at full speed, with a .375 H&H. Hit just far enough back to save the cape.
