I wouldn't expect a new board to all of a sudden make you better able to go fast. I have the Proto, same dampening as the Evo, and have only felt sketched approaching 50 mph a the bottom of a headwall. If you are set on getting a new board, try to switch up your brand to give something else a chance. Maybe a Lib TRS? Or a Niche Aether? Maybe a Arbor Westmark or Element?
A little stiffness will go a long way. If you have to stick with NS, the SL would be all the board you need for a while, I'd stay away from the Heritage. The Cobra is a pow board, so not the best choice unless thats all you are riding.