A better question would be what are my goals and how much head room do I want to run. I don't like the notion of running injectors above 90%. Since you have them in your signature, you probably want to log your duty cycle now and see where you are.
OP...650whp is the common thought. Playing with fire beyond that and will need BAP, larger injectors, or return system depending on the fuel you are using (e85?).