With 300cc/min injectors at 85% duty cycle (you won't get near to this) you're flowing 255cc/min per injector*, so 1020cc/min total.
*Assumes a linear relationship between flow and duty cycle.
1020cc/min = 61200 cc/hour = 61.2 litres/hour.
Add 20% headroom and you're at 73.4 l/hr, still within the spec of the OEM pump.
So 156 l/hr is plenty big enough, I'd avoid going too large, as the regulator can only return so much back to the tank and throttling back a beefy pump can do it more harm than good.