If your application happens to share injectors with say a 320 hp version it is somewhat possible (I would think) that you are at the max of what fuel the tips can deliver. at a given psi, you can only cram so much fuel through a certain size of hole.
I am no authority and have never been in an A model pump or governor but something else to consider would be the torque rise (or lack there of) available from the governor. Unlike most other common engine brands found in road tractors, Cat's b/c governor works somewhat like the governor on a farm tractor by adjusting itself to maintain a given speed matching throttle position at cruise. In other words, your foot stays in the same place when you hit a rise in the terrain but governor adjusts rack accordingly to try to maintain the given speed. The amount of this compensating feature is not a real high percentage and can accidently be defeated by mis-adjusting the rack travel screws(or removing them both)
Instead of allowing the rack to pretty well fly wide open in an effort to maintain engine speed under load(the way an old farm tractor will) the amount of compensation would be (this is just a s.w.a.guess) under 20 % but when working right is a big factor in the way a Cat pulls. That said it is also smooth and suttle enough you don't really notice it happening so much. Just a slight increase in boost and maybe a little extra wisp of smoke as you ascend the rise. But if in some way you defeat the torque rise feature you will know it even if you have increased fuel settings.
1. research the type of governor you are dealing with here. Increasing fuel delivery available may result in no noticable power increase if the governing system is restricting power to some given level based on inputs (especially if torque rise has been defeated) (assuming your tractor even has such a feature)
2.In the case that injectors are pretty well maxxed out at the tractors's factory spec, a huge and noticeable difference may come from increasing injector size-even if you put the screws back to or near stock (ask me how I know) Of course, you may quickly surpass the efficient function of your turbo at such a level and then here comes your higher egt....
3. I am no pro. just throwing out some ideas while eating breakfast and any contradictory views will not insult me especially if coming from the small handful of pros left that visit here.