Ok,
technically there was a variable introduced in the test.
However, to me it was just another test to prove what's already been proven many times before. My research has included reading numerous articles about this, "Turbochargers" by Hugh Macinnes (which has a section on diesels), and personally modding the turbo, induction system, and exhaust of a Mitsubishi Eclipse. I tend to overresearch things, and I have NEVER found any valid information stating that restrictive intakes or exhuasts are preferable.
Improving the exhaust flow after turbo can significantly reduce the backpressure the turbo is working against. This allows it to spool quicker & extract more energy out of the exhaust flow.
On the compressor side, that increase in energy gets tranlated to higher boost pressures, higher flow, and heat. One way to increase the power output of a turbo'd engine is to increase the boost. However, the only number that really matters is at the inlet valves. Any intake system has some restrictions, and the compressor needs to produce higher boost to compensate. Getting rid of intake restrictions effectively increases the boost without requiring the compressor to work harder.
Stock intake systems are generally poorly designed, with many restrictions. Rapid changes and even reductions in cross section are common even in "performance" cars. It appears that packaging invariably takes priority over performance. Why waste your gains pushing air through restrictive piping? All that accomplishes is to require the compressor to work harder for the same performance, which produces more heat. That heat raises EGT's, and also forces the cooling system to work harder.
Stock intercoolers are generally undersized and will saturate after a short time. The resulting increase in charge air temperature decreases air density, and will reduce power. It's been known since the '70's that intercoolers improve efficiency & performance. Why run one that doesn't cool the air?
Mods to the exhaust & intake are relatively cheap if you do the work yourself. Every expert I've read lists these improvements as a FIRST step. In my case, I can build a restrictive system or a free flowing system - they will cost essentially the same.