[Steve Tinker]

Yes,
I live in a fairly hilly part of eastern Australia where long highway 2 mile hills are quite common. At the speed limited 110 km/hr (70 mph), the engine is turning over @ less than 2,800 rpm - well off the peak torque or power curve. If I accelerate up the incline at those revs, there seem to be something lacking compared with the original pipes. Over 4,000 rpm it equates to the old original system of header / pipe combo.
Now I know this is a seat of the pants, non scientific appraisal, but I've owned this car for nearly 4 years so I have a reasonable understanding of its capabilities in these conditions.

I guess the only real way is to compare dyno data, but those things around here in Austalia are as rare as hobby horse droppings.....

There's an old racers story that if you give him more HP he never complains, but reduce the HP and he'll let you know big time - the missing neddies are obvious!!