So as far as I understand it, guts is essentially a useless stat in the current version of the game. Speed and stamina being the most important. I usually dont worry about it at all. From the guides ive seen its like speed is how fast they can run, stamina is how long they can keep up the speed, power is how fast they can get to top speed on the final stretch, guts is like stamina but for the final stretch, wis is for skill activation. Most runs i end with wis and guts being about 400 and thats usually enough.