You don't need bigger injectors unless you plan on running more boost/power than the stock injectors can handle. It is somewhere in the 230whp range. At least at 100% duty cycle. I believe there is always a little headroom, and I am sure someone has put down more than that with a piggyback or standalone running
If you are planning on running more than that, I doubt there is an FS left that will last very long on the original internals.
You at least need a piggyback and you can get some very good results, but when things start going wrong with it, you just have to pop the stock injectors back in to remove or bypass the piggyback.
I kind of put my limit at the injectors since I know I am just asking for headaches and large "investments" if I go past them.