The 450s would be ideal because they'll leave you some room in case you want to go to a standalone and turn up the boost later on. For now, with the 450s, you can run them with up to 10lbs of boost without the need for a MAP limiting device(check valves, voltage clamp). If you run smaller injectors, you'll have to run those with less fuel trim(probably ~-30% or so), and that cuts the MAP signal less, so you can't run as much boost without a MAP limiting device. You don't need OBD-II injectors, just the clips to go with the DSMs and a resistor pack. Actually, if you can't find clips, you can just cut the little post in the middle of your stock injector clips off, and they should work fine with the DSMs. This might save you a couple bucks and the trouble of soldering the DSM clips onto your harness.