We have been using 600cc/min injectors on all our Stage 1 Supercharger Kits as well as our Turbo Kit without running into any fueling issues. Here are some dyno graphs displaying the AFR with different boost levels. All these graphs are with 600cc/min injectors. Notice the 600whp graph starts to taper up at the end due to maxing out the injectors.
So, if you are running out of fuel, I would definitely perform some of the basic checks to make sure that you have a good fuel pump and base pressure. Also, we use a 255lph Walbro Fuel Pump (GSS-342) in all our kits. To my knowledge, Stillen doesn't use that part number, and I'm not sure what the rating of their pump is...you may want to check with them on that.
Phunk brought up a few good points as well as far as the supercharger's parasitic horsepower loss...especially on the Vortech unit.
We have made over 460whp on our supercharger kit with 600cc/min injectors without issues. However, on our Stage 2 Supercharger Kit, we elected to go with 650cc/min injectors and a fuel pump voltage stabilizer to give us an extra margin of safety.
One final point is that there is a direct relationship between the K multiplier, MAF voltage, and target AFR. Just make sure that whoever is tuning the car is well aware of that.
As you see, we always post our AFR on our dyno results so that there is no question that our tunes are safe and solid.