a no 1 tip is about the largest you should need based on what your talking about, i dont know what your talking about with the no 6 and no 4 tips, you scrapping out a m1a1? With the proper tip size and regulator settings you can get alot out of a bottle of oxygen.

I would use the #0 tip. The kerf on your cut will be much smaller. On my Victor regulators I run my Acetylene at 7lbs. and my Oxygen at 20lbs.