clodbuster, Ammo manufacturers do a lot of testing to find the "right" loads for each cartridge. When handloading, I've always found matching the factory load is a good starting place for optimum accuracy and function. Usually factory loads are well under maximum pressure.
When you load "hot", (near max pressures), you will dramatically increase throat erosion (barrel life), stress other parts of the gun and probably won't get the accuracy of a lower pressure load.
A slow burning powder can develop the same muzzle velocity as a fast burning powder. The difference is the slow burner will do it with a much lower chamber pressure.
For most any given cartridge, there is a powder with the right burn rate that will give the desired results without coming close to max pressure. In fact, many lower pressure loads will chronograph faster than max pressure loads. In other words, max pressure does not equate to max power or max accuracy.
