If you go larger then you need to have a way to control them, otherwise you'll flood the shit out of your motor. Stock turbo injectors are 440cc's and will support 400whp. Before we can answer your question we need to know what you want out of your car and what your budget is. Simply putting larger injectors in will do nothing for performance, unless you a)need them, b)can control them.
FWIW, I'm running 1000cc RC's now
