There are more things that go into "better injector than xxx" than spray pattern and winding size. More importantly minimum stable duty cycle, linearity, and void time. Dig up the Mazworx blog post on that sometime. The difference between big Bosch injectors and the Injector Dynamics data is ludicrous. Not to mention that I've never even seen similar data for Denso (PE, Sard) or JECS (Nismo, Tomei) injectors.

For "350-400whp" cars, use something in the 740cc range. 550's will run out somewhere just past 350whp, even though internet hardasses say that their buddy makes 4 million on 550's. Going larger than 740cc is where people start to have idle issues (depending on car and tuning). 850cc Sards idle well from what I hear. The 96# (1000cc) Bosch injectors have a questionable idle. Also, I'm not hearing good things about the RC 750cc high impedance injectors overall.

Just buy Nismo/Tomei 740's and be done.