2530 is too small for 250rwkw, expect around 200-210rwkw, 2535 will give around 230rwkw.... Injectors start to be the limit around this power give or take a touch...
I'd be worried giving my car to a mechanic who thinks he can get 300rwkw out of stock RB25 injectors.... Or maybe he has a happy dyno that reads about 50rwkw to high.
I also think once you start going over 250rwkw or so you're going to run into reliabilty problems, going off your first post, and your priorities, i'd stick with the 2530 or 2535, stock injectors and a safe tune, which will give you a very nice 210-230rwkw (or more if his dyno reads high?)... very usable.