Rendering of One Vanderbilt to the left and Grand Central to the right, looking north from 42nd Street up Vanderbilt Avenue. Image courtesy Kohn Pedersen Fox Associates. As currently proposed, supertall tower One Vanderbilt will rise to 1,350 feet—1,450 at its peak—to become the city’s second-tallest building. But its top wasn’t the focus of today’s Landmarks Preservation Commission hearing. It was its bottom. The LPC met today, not to rule on the proposed office …