SMB, I agree with your plot, looks totally reasonable and around ~38 lb/min at ~112F with PR loss of the system (which I am well aware of.)
You guys can calculate and graph all day long, but the results speak for themselves. Up to around 15 psi of boost, the N54 gains between 12-15 whp. That is impressive. This means regardless of the math, that the entire system still has quite a bit of headroom before flow starts becoming a problem for the smallest "bottleneck" which appears likely to be the hotside. I used to do the same thing back when I was relatively new to this, and would not consider notions because the math wasn't spot on. That's how you go slow. The innovators get their noses out of the books and calculators and actually test things in real life.
Anyway, I leave you with this. Many of us owned chipped 1.8Ts at some point the past. Its been proven without a shadow of a doubt that chipped cars have great turbo reliability. Many of them going well over 100k miles on the stock turbo. Chipped cars run nearly 20 psi in the midrange, tapering to 12-ish up high (around 6k).
Here is the standard K03 mapped for the 1.8T with completely reasonable VE (90%) and 12 psi. These turbos make 40-50% more power
at the wheels than the compressor map is even mapped out to....and they last. I have no doubt that the Mitsus will be similar and early data supports this, IMO.
OMG, what were the tuners thinking? There's no way that turbo can support that flow and last, etc, etc, etc. It has, and it does...and does it well. Enjoy.