I love stacks and how they look and sound, but well a properly built and routed airbox is always going to out-perform open stacks full stop. Unfortunately in this chassis and most engine configurations (for appearances), open stacks wont take advantage of a proper high-pressure zone in an engine bay ( lets say in this case, the base of the windscreen at the bonnet or the front of the car).
So, the tests done above in a near flow-less area on a dyno (assumed with a fan) of course the longer stacks are going to provide better flow as its going to 'charge' the intake flow better in each tube.
If using open stacks, understanding how the air behaves as it flows in and out of the bay is equally important, as air has the ability to push itself in to the throttles, and subsequently suck it out if the design and zone permits. Not a big deal on a stock motor, but that's why some ITB's use a curved ram tube (like stock) to maximise the air in, but to prevent loss of pressure or suck-out.
hard to explain without graphs and CFM data and a bucket load of images, but you get the basic idea.
If running open stacks, it would be wise to use decent cold air routing and to do a bit of crafty ducting to harness the high pressure zones to trap alot of air without a shitload of drag (not that its really going to be an issue).
Open stacks do outperform the factory air box setup though, but u do agree a well designed intake can work better than just stacks alone