Test data from engines.
 

IQPC Advanced Charging & Downsizing Concepts Engine Turbocharging

Here you can download some test results related to engine efficiency.

On diesel engine section there is a turbo diesel with cars exhaust pipe vs straight pipe there is over one second difference in turbo spooling in favor for the straight pipe.

There is also a clear benefit from smaller turbocharger to acceleration times at lower revs.

...SMALLER turbo = more TORQUE sooner in RPM curve.

...BIGGER turbo = more HP later in RPM curve.

Twin-Scroll = Fun :D

Nice resource!

...HIGH-ball plus LOW-ball = ALL-ballz fun (ha,ha)!