My only suggestion would be to ditch the hush kit as well. You might pick up 3-5 fps with your setup. Also make sure that the bow is tuned very well otherwise you will lose some speed there. If I am not mistaken the Libertys are now being shipped with eliminator buttons in shrink wrap both above the single cam and below the idler wheel to optimize the bow's speed potential.

Just to ease your mind, with a 71 lb, 30 inch draw length Liberty and a 430 grain Easton Axis (hush kit installed as well as a medium sized Shurz a Peep, string loop and two tied-in nocksets) I am getting 268 fps out of the bow.