And you can get them right (ninja reg at least) right on 3K but it takes a bunch of different size shims. Some are thinner then paper. A .001 shim can raise output by 100psi when you get up that high.
These .047" bellevilles are the ones I use in high output regs. The .032 or .022 are too thin (even doubled). They are tough to get right on the number you want.