a restriction in the throttle body limits air flow, and 2. Yes, the engine could operate more efficiently with increased flow, meaning larger diameter piping, but what good is that when 1. This is true as well for the turbo exit - intercooler piping, and it being no larger than the turbo outlet on the turbo side of the intercooler, thus retaining as little pressure drop as possible, while keeping velocity high.
So theory has led me to believe there is no reason to go with piping larger in cross-sectional area than the area of the throttle body inlet minus the butterfly at full open. This reduces pressure drop, keeps air velocity high, and unless an aftermarket or q45 throttle body is on the car, offers best air input to the engine on the stock throttle body. Also, larger 3" piping after the intercooler seems to bottleneck at the stock throttle body, and the best gain/balance is 2.75" piping from intercooler to throttle body.
however, this air loses velocity and at higher rpm the engine cannot feed itself fast enough, lowering the power peak of the car by an unknown factor of rpm.
What I have found so far is that opening up piping diameter after the turbo will flow more volume, and allow the charge-air to expand as it flows creating a venturi effect which cools the air further. I ask because i've been trying to do some thermodynamic fluid simulation to determine optimum size of intercooler piping.