The 2.7 (315hp and 350ft-lb, 13.6/9.8 ) has 10 more hp and 70ft-lbs more torque than the 3.7L, but matches the fuel consumption of the less powerful 3.5L (285hp, 253ft-lb, 13.7/9.6)
But I think people have unrealistic expectations of turbo engines. If a person is using 300hp, they're going to burn 300hp worth of fuel. But at lower or no boost, as in a steady state on the highway, the smaller engine should be producing better fuel economy.