Yeah, the most I've called for so far is 3700 on the B-codes, and I've never seen a mechanical guage jump that fast.
My hot program runs 3000-3100psi depending on the exact conditions and the IPR duty cycle never actually makes it to 35%. I'll have to turn it up to 3600+ and see what the duty cycle is. But if you really just wanted to, you could run 3800psi until the stock pump hit the relief at pretty much whatever duty cycle you wanted, with any injector you wanted, with just a simple change in pump displacement.
Not that anyone would want that I guess. But it's there if needed.
I'll go turn it up as far as the 6 gun will let me until I hit 1500 degrees again, and I'll see what the duty cycle looks like.
On Edit:
The duty cycle runs 44-45% at 3600-3650psi ICP. BTW, my personal system is running the lowest displacement configuration of the G3.