You can use this calculator to figure out the right size injectors...
RC Fuel Injection
The 600 cc's may be fine for the stock levels of boost, but maybe not for the upgrade?
Another possiblity: I wonder if your K values for the injectors need to be adjusted?
It could be that you do have more room with the injectors, but if it's all calculated based on the K values, possibly you can go beyond "100%", and everything just needs to be rescaled a bit.
Double check that all the values modeling the physical parts are correct -- after that, it's either injectors or pump.