Assuming the C16 is used, the primary advantage for a 917 D3 is getting it optimized to your swing. What my fitter has done with the 917 D2 for me was worth the time. I thought I knew what I was doing with the 913, but he got me 20+ yards and a tight dispersion pattern. The 917's have a lot of the technology from the C16. The choice comes down to personal preference.

Personal preference and cost. The C16's are not cheap.