The throttle linkage in the pump is all on a set of springs. The difference the rack sees in the pump (controls the amount of fuel delivered) from half throttle to full throttle may not change, depending upon plat design and position. You could get great mileage with no plate or AFC, or terrible mileage if you have both of them full back. Depends on how your drive. You will get the same mileage at the same speed regardless of which plate you run, because it still takes the same amount of fuel to keep that speed up. Its when accelerating where difference becomes apparent.

 

A fuel plate will not change your cruising MPG, it only dictates how far the throttle can go at its maximum point, as I understand it. Someone correct me if I'm wrong.

As for the turbo, post a pic of it.