...VERY short backswing and huge acceleration.
That part of your post makes me think heavier would be better for you.
I am currently trying an original Icon in an SMT head & I like it so far.
I also have a 525GRT at 9.5° - when I got the head, the only shaft I had sitting around un-used was a S300 DGSL. The head was used & the previous owner had added a little weight - with the steel shaft I'm estimating my swingweight up around E-2 ?! This thing is a hammer! I'm getting the urge to try a different shaft in it, but its really working well for me - I should probably leave it alone. ( but I probably won't

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My point - if you are aggressive thru impact like you state, the heavier steel shaft might be very good for your swing & I'm sure it would bring down the spin rate. Have you had a steel shafted driver recently?