Having recently had my engine re-built, I went for the WRC 8 injector route purly for emmisions. There are more and more Police carring emmision testers in their cars and because of the "Greenies" pressure fines are now quite high.
As you can argue that the car can only be tested to the same as MOT standard (on tickover) 8 injectors gives you the best chance of passing with a tuned engine.
Maybe I wasted my cash, but at least I feel safe if pulled over.