Interesting. I'm currently a 17 index and I had a rare round yesterday with zero double bogeys. (I did have one triple.) After the round I was thinking how unusual it was for me to shoot 85 (especially with a triple) with only four GIR and 3-putting two of the four. I attributed it to avoiding bad holes (except for 1, lol).
That's true, and I had 17 GIR +1 which is what kept me from getting double bogeys. I know that has to be an unusually high GIR +1 for me so the potential benefit of focusing on it makes sense.