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I did exactly that on my 07 SG (13" shocks with a 1" lowering kit) and it improved the ride immensely. However, I have not found very many sources for lowering blocks for the 09-up frame. The swingarm changed, and the prev blocks don't fit the same.
If you can find the parts cheap, or at all, it may work well for you. However, you have to consider thats about $200-$300 that could be spent towards a nice set of Ohlins. I personally would not recommend Progressives. They are a decent shock and improve handling, but I don't think they improve the comfort of the ride much, and have pretty harsh rebound damping, that cannot be adjusted.
My first recommendation is to ride the bike as is for a thousand miles, let the shocks break in a bit, and experiment with air pressure. (a pound or two plus or minus can really change the ride) The 09-10 SG shocks are a LOT better than 08-older versions.
Ride the bike and play with it a bit before you spend money fixing a problem you may find you don't have.
You might try 12.5" Progressive 440's. Keep your eye on the classifieds, people are always looking for the Holy Grail shocks. Probably find a used set in the $300 range. These will ride better than your stockers. There are always people looking for your shocks for their Road Kings, so you could sell yours easy too.
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