Dynamic gold S300(stiff) is equilavent to Rifle 5.5. Swing speed 95 to 105 mph.
Golds have a high kick point and the Rifles vary by Flex coefficients. The lower the number the more flexible the shaft and the lower the bend point. I.E. 4.5's are going to have a lower kick point than the 6.5's. I have played both and each are good but I prefer the Rifles. Very smooth and great feel. It will run you about $8-10/shaft more from factory for the Rifles. Now the Flighted Rifles have a progressive bend point. The longer the iron the lower the bend point, which would help the longer irons get higher.
I have the spinner shafts in my SW and GW. The idea behind the design construction is to simulate a late release which should inpart more backspin. I personally do not see a large difference.