You have to keep in mind the capabilities of your fuel pump too when you talk about that large an injector.
Assuming you have a walboro 255 like most of us, that's 255 liters per hour, or 255,000 cc's per hour, or 4166cc's per minute, or 1042cc's per injector on a 4-cylander per minute. In other words, a walboro 255 fuel pump cannot supply enough fuel to feed 4x 1200cc injectors. More realistically, fuel pumps aren't designed to work at 100% capacity either. The maximum flow capabilities also vary with how much gas is in the tank, etc. In tank fuel pumps are somewhat limited. If you are seriously considering injectors >850cc, you should be looking into a dual fuel pump setup or preferably a fuel cell.
The stock 02-05 WRX fuel pump is about 140lph and was paired with 440cc injectors. This is about a 75% fuel pump utilization at 100% injector duty cycle. The STi fuel pump is about 180 lph and was paired with 560cc injectors. That's also 75%.
Holding Subaru's 75% usage in mind, a 255 fuel pump should be good only to 780cc and a 300 lph pump would be 940cc. I think you can push it a little beyond that because we generally don't want to run our injectors at 100% either, but I wouldn't go much beyond 75%. A 300lph fuel pump would work fine with 1000cc injectors but I wouldn't go beyond that.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD