the 555cc and 740cc are about the same price. I was going to go with the 740cc but the sard 850cc worked out cheaper even with the required coller. The bigger injectors wont use more fuel, they will just work at a lower duty cycle to produce the same flow as the smaller injectors. The fuel comes from the tune not the injectors. The bigger injectors just allow more fuel to be flowed based on a tune
As mentioned above, you may want to look at a Z32 AFM is you dont already have one.