Yeah I liked the SuperGramps build! They are bonkers! "Turbo Yoda", "Dose Vader", "Skids", "Chopped"
CAI results depend on how restrictive the OEM airbox is, but if that Skyline has a MAF sensor, they should really retune the ECU accordingly to get the most accurate results. It can take a few runs for the ECU to adapt and retune the fuel trims.
People do see gains with intakes on the GTI though, but nothing earth shattering.