Yes, "full boost" is required to achieve 310 lb-ft of torque, but you don't need anywhere near 310 lb-ft of torque to maintain cruising speed. Boost pressure is controlled independently of engine speed.
Throttle opening, valve timing, ignition timing, injector pulse width, EGR, and other parameters are constantly adjusted to produce the desired amount of torque in the most efficient way possible. There are times when the throttle blade may be wide open even when you're pressing the accelerator pedal half way while the turbocharger is developing no boost IF that's the most efficient way to develop power at that given moment.
On modern, turbocharged engines, the acclerator pedal is actually a "torque request pedal" that commands many different systems to do different things to develop that requested amount of torque. The throttle blade is no longer directly connected to the accelerator pedal. Some systems, like BMW's Valvetronic technology, keep the throttle blade wide open at all times and use valve timing to control output while closing the throttle blade only as a failsafe device.