Just so you guys know I stuck the thread because it is one of the BEST on intake systems bar none.
Darby that is well and truely over my head. While i understand the basic principles and theories you've reached a new platto, good on ya!
From what I've been able to dig up on the top hp cars using forced induction, ie turbo in this case, the shorter the runners and size/shape of the expansion chamber does make a difference. While what i can explain is turbulance, but not the indepth you have. It seems from what I've been able to find a larger frontal area of the plenum and sloping down to a smaller rear section is what seems to be the go for these application. The area I do agree must be able to support much more than what the individual cylinder capacity is. This is without a doubt common sense in the intake world. While I'm not designer for intakes, I go by what I see the top cars using.
To be able to squeeze 1,400+hp out of a 2.6 - 2.8 litre motor they all seem to use the same basic shape plenum. Keep in mind all these cars are using extremely large front mounted intercoolers there for the intake charge temp is greatly reduced. What you don't want is the air inside the intake system to be there long enough to then again re-heat up. This in fact would negate cooling the intercooler is doing and you get no gains.
In keeping with the high rpms for a mass produced turbo motor to rev to 8,200rpms factory you then can see why the shape, size, and runner lengths are what they are. HKS, VEILSIDE, JUN, TOP SECRET, etc all use plenums of nearly identical shapes and configurations. All have cars making extreme amounts of power using gas (race gas but still gas).
Most high performance plenums I've seen for the RB series motors are extremely thin. They would be in the area of 1.5mm - 2mm thick. Why I have not idea other than weight savings.
Something else has been sitting with me. You've memtioned the "shockwave" effect of the valves opening an closing, while that would be an issue with an N/A engine, when you have the intake system under constant pressure this would be reduced. Air compresses only a given amount, and even at that the amount the valves would move I honestly can't see it making that much of an impact on a forced induction small capicity engine. The larger N/A motors with very large lifting valves, which are also much larger would make a lot more sense.