you may want to go to a dyno that has the ability to measure air:fuel ratio across the entire rpm range and can print out the results.
Air:fuel ratios are one of the things that tell us whether we need to upgrade fuel or not.
If you think you are running too lean on the air fuel ratio at one part of the rpm range, risking the chance of detonation, then you may need to upgrade the injector.
If you can't get to a dyno, then learn to read your sparkplugs IMMEDIATELY AFTER A FULL THROTTLE RUN (no idling after the run...pull over immediately after a WOT run, shut the engine off immediately, read the plugs). This also tells you if you are running lean overall or not (white flecks).If you idle or drive around after the run, you will be reading the the state of the air:fuel at idle or partial throttle and not WOT.
What are the other factors that tell you if you need to upgrade the fuel system?
When you first determine the power goal you want, you can then calculate how much fuel you will need if your engine can deliver enough air (cylinder filling or volumetric efficiency) to get that power goal.
If the injector flow that you need to get that power goal cannot be met by increasing the fuel pressure by 20% max. or if the time that the injector is open (called duty cycle) exceeds 90% (of the time for an intake stroke), then you need a larger injector.
With the air delivery modifications that you have, your volumetric efficiency can be met with the stock 240 cc/min injectors that you have now using stock fuel pressures. Running an injector too large will result in an overly rich air fuel ratio. This not only reduces power but also may wash the sides of your cylinder walls with the excess fuel dumped there by a too big injector. The walls lose their texture and oil and you get early blow-by and loss of compression.
if you want to learn the equations or calculations for the flow size of injectors needed to make a certain hp (assuming you have enough air flow to get that power first) or how much to increase your FP by to get a certain injector flow, check out the RC Engineering website's tech section: