The difference between attempting it on 4th and attempting a FG was an added 2.1 win percentage.
Harbaugh said “So what’s the added win percentage of going for it? He’ll give it to me like one, two, three, four, five, six, up to whatever. Then you just decide if you want to do it. It’s not strictly based [on the numbers]. I listen to it. If he starts telling me 3 and 4 percent, I get really interested. If it’s 1 or 2 percent, I’m still interested — especially if it’s short, if I think we can get it.”
I'm wondering what the risk is for the remainder of the game if we failed to get the first down (because i think that is the most likely scenario) compared to kicking the FG. What would the win percentages say then? I think that also should factor into the decision, don't you? For example, if it says cutting it to 4 point lead increases win percentage to 19% vs win percentage decreasing to 8% if you fail to convert on 4th down. Wouldn't you like that information to be taken into account as well when making your decision?