Assuming the head weights progress in 7 gram increments like they are suppose to and there will be no tip trimming, just taking the #2 iron shaft, putting it in the #5 iron and cutting it to #5 iron length, it should play close to a full flex more flexible, S100. I calculate that by knowing that if there a 7 gram increments in the heads, then there is a 21 gram heavier head (254g std. weight #5 iron vs a 233g standard weight #2 iron) going on the shaft. 2 grams of head weight is approximately 1 cycle of flex (in frequency terms). So 10 plus cycles difference in the 21 gram head weight difference. 10 cycles is a full flex. S100 is a full flex softer than X100.