I‘m talking about small blocks. I have 1.625, 1.750 and 1.875 to test. On pretty much a stock 360 and then on my 340.
I say the 1.875 header will make the most power on both engines and it won’t kill any bottom end.
I have tested this before so I already know the outcome.
The time slip can lie to you just like a dyno or a flow bench.