So guys I am putting in a new rotating assembly for my 2011 Mustang GT, I'm trying to decide what compression to use for my pistons, I am trying to do a max hp NA car.

 

I don't really know the answer to that, but I can "help" by suggesting that you might get more response if you post this in the 2011-2014 GT section with a more descriptive title

regarding the pistons -- I think the original compression ratio is about as high as you can go, without needing to always run high octane gas, but I am not sure about that