At 6000 RPM you have 21ms of injector duty cycle to work with. If I recall, the stockers are indeed about maxed-out using somewhere around 18+ ms at 6K on the stock tune. If you go larger, you'll need to change (scale) the injector duty cycle via SCT (or VEC, AEM, other) in order to dial it in to your 'actual' fuel demands. I think the stock fuel system can support a bit larger fuel demand (since you aren't dramatically increasing your fuel needs). Its too bad the stock injectors don't have much additional flow to work with.
"Aspice, officio fungeris sine spe honoris amplioris." (Face it, you're stuck in a dead end job.)