Both are 42.5" long.
913F 13.5 D3 setting (14.25*) Diamana S70+ stiff with stock headweight. On the machine with this shaft it was 219 carry and 242 total.
915F 15 A3 setting (16.5*) Diamana M60+ regular with 14g weight. The shaft originally was from a 915F 18 but had a 1/2" extension added. This club originally had the 70g shaft I currently use on the 913F. With the stiff shaft I had 220 carry 247 total.
With the M60+ and a 15g head weight on the 913F, I've had a couple occasions where I have hit a small draw 250 yards.
The 915F fairway performs better vs the 913F with the M60+ shaft. The latter has a small fade and the former is straighter but with an occasional small fade. The former feels more solid. Heavier head weight is better with this shaft.
The 913F fairway performs better vs the 915F with the S70+ shaft. Both are pretty much chalkline center. The former feels more solid. Stock head weight is better with this shaft.
The higher ball flight with the M60+ was as expected.
The 913F performs better with the 70g stiff and stock weight vs the 60g regular and 15g weight. Not much of a difference in feel.
The 915F performs better with the 60g regular and 14g weight vs the 70g regular and stock weight. It feels more solid with the 60g.
Can understand the possibility of the 60g being hard stepped as a reason for not much difference in performance.
Why would I have a small fade with the lighter regular shaft? Tighter pattern with the stiff?