It depends on the power your looking to make.
Say 400bhp, with a max duty cycle of 90% you'll need 622cc, that doesn't take into account fuel pressure. However I very much doubt you'll be able to stretch 550's that far unless you push over 4.5 bar fuel pressure which isn't recommended.
It also depends on the ecu your using as to how good the injector control is. Anything more than 550's I would be looking for a good standalone tbh.
Injectors aren't cheap either, best to spend the money on some good ones because many large injectors on small engines make them run like a bag of shit.