STI injectors don't have great output. Not many people run them down here because they run higher duty cycles than at the same horsepower than Nissan/HKS/Tomei/Nismo injectors. My GC8 STI 440CC injectors were maxing out were my 370were maxing out, a few cars down here are runing 525cc injectors, they max out like if they are a bit smaller than 440's. IDK why, but suby injectors just don't seem to have a great output. Kinda reminds me of DSM/Honda topfeed injectors.
So I do agree with you there.
Edit* I'm guessing Andreas already knew this;
This is a conservative rating at 3 bar. * indicate side feed or top feed inj sizes that can be bought from Nissan, Nismo or Tomei. Alot of the sizes you can not get but are there to help you if you are looking at a cetain flow rate by going to 4 bar.