Yes there you go.
The larger prop and more pitch will increase the Amp load. The old saying up an inch down in pitch or whatever doesn't apply directly to electric planes. For fuel engines you have a peak torque and RPM range you want to keep the engine running in to get the best performance from it. You have more torque and adjustability in an electric system. So look at the problem from a load point of view and relate it to the models performance or intended use. Voltage is king and being able to add more voltage will decrease the Amp load. So any time you can run more volts that will be better performing and more efficient.
So for you if your limited by space or weight to run 6S thats fine. Now test props to get to 1100-1400 or so Watts.
How many pounds does your plane weigh? AUW (All Up Weight)
Another indicator of model performance is the power to weight or Watts/Lb. For a scale model your shooting for more than 100 W/Lb and opinions vary on what this ratio should be.
A simple reality check is to look at the HP claimed on the engines you would normally run on the plane. Then convert their number to Watts. So 742 Watts per HP. If you would run a pair of engines which have a combined 4HP then 742 X 4 = 2968W. So 1400W is close to 2HP per motor for this plane.
I dont know the planes specs but knowing how to convert in and out of fuel engine specs and relating them to electric power will give you a good perspective on what you need to get similar or better performance than fuel power.