Hi,
my training is in Physics and Engineering, and I would agree that the max thrust is acceleration plus cutting thrust plus friction.......and that's fine until you are standing in front of the
machine. The transient forces are many times your calculation.
My estimate, from personal experience having built and operated a machine of similar size and capacity to yours, is that 20mm is marginally to small, 25mm is about the best balance and that 32mm
is marginally larger than need be. That's not a theoretical calculation but an observation of reality.
Your money, your choice.
Craig