Factory injectors are barely adequate to even feed a stock motor when they're new, chances are they aren't feeding enough fuel above 5500 any more. You will want to upgrade your injectors before doing any other upgrades.
FWIW I don't believe this is true. Everyone seems to say it, but no one seems to have tested it. When I installed an M30 AFM and K&N cone filter on my car I also installed a WB O2 to see how the engine would adapt to the mods. When I first drove the car after I swapped parts it was evident that the car was getting more air as the AFRs were reading leaner than they were with the stock airbox and AFM. However after a few km of driving the DME adjusted the fuel trim and the AFRs were normal. Then I did some pulls up to 6500rpm. At WOT near redline the AFRs were in the low 13s which is fine for a n/a car. Now this isn't to say the injectors weren't near 100% duty cycle but even with increased air flow my old, dirty, stock injectors were able to flow enough fuel up to redline.
All of that being said....
The 19# injectors are a good mod for anyone who's looking to get a MarkD chip.