Ds Adapt vs OPTM? What are the Denali shafts?

Alright so I have the cobra iorns picked out, yesterday I went to the PGA superstore and decided I want to hit the DS adapt and the OpTM one last time

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I took my current driver with me! I hit the DS adapt and something felt off, wasnt getting the yards like I thought I was etc, go to my regular driver I'm hitting it farther and better,

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I try the OpTM with the same driver shaft I have now, what I didn't know is that when I tried the Ds adapt driver it was 65g shaft and I have 55 in my current RBZ Taylor made,

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Had them out a 55 on the OPTM and I hit the ball better farther etc!

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My question is the guy at the store told me you can't change out the shafts to get the 55g for the ds Adapt but you can only do it on the OPTm! What is the difference between the new Denali 60-50 shafts, because if I can order the 50 g on the DS adapt I might go that route?