takafam, thanks for the nice comments.
Here’s the deal on this one. The DG SL S300 is about 20 grams lighter per shaft. This means that after a reshaft at the same length, the swingweight will go down by approximately 3 points. My recommendation would be to put at least 2/3 rds of the swingweight back which would be 2 swingweight points. You should be able to swing this lighter overall weight club a little faster and coupled with a little more head mass (weight) you should get 3 to 6 yards additional distance. This is theoretically how it works. However, the big factor here on what will happen to you exactly will depend on what trajectory change, if any, you get. This asks the question; is your trajectory with the ball your using the ideal trajectory? Only you can answer that.
I don’t think the GS 75 will help you since it is very tip weak (soft tip). This would be a radical change for you, however, once again are your current shafts too tip stiff for you? If yes, you may want to try this. You would also need to add some serious weight to the driver head because of the greater shaft weight differences.
Note that the SL shafts are also tip stiff and play close to the heavier Dynamic but with the advantages above.
Let me know what you do and what the results are.