im running 07 injectors also. and a stock STi fuel pump. on my last tune, i was running a little lean at 19.5psi but we retuned it to 21psi and richened her up a little bit. i dont think i would have gone past 16psi with my stock injectors.
check out XPT Tuning. the owner Braden tuned my car and several of my friends as we know him personally. he is WELL known among the opensource community. and he know his stuff. i dont know what exactly his tuning methods are but its pretty impressive!
XPT tuning has a bunch of "fully Tuned" maps based off of cars he tuned that are specific to mods you have. i believe recently he added Lauch Control to All 02-05WRX.
you have the 2.5l you are going to have some impressive numbers with a good tune especially with the TQ numbers!
for those who doubt my tune and think i am lying, i can Send you my LOGS!
the biggest question that no one has asked that needs to be asked is:
what octane fuel?
good midwest non-Ethanol mix 93 you can run as high as 22-23psi w/o issue on a VF39 IF you are properly tuned & have proper heatsoak prevention/intercooling. You will need a GM BCS or other 3-port solenoid or a MBC to achive that high of boost.
You may or may not have enough fuel w/ the 550cc injector to support that much boost.