statjunk - For what its worth, here is my method of picking a load for a new cartridge.
First I review several different manuals and compare their 'most accurate' load. I look at posted velocities and amount of powder used. I like to choose a powder that give me good velocity and fills the case to just below the neck at maximum charge. (I don't start loading at max. - this is just for reference.)
I then load 10 rounds starting at 10% below max and work up in increments depending on the max charge. This could be 1/2, 1, or 2 gr increments.
If the first powder does not produce acceptable accuracy I move on to the next selection. Sometimes I found that it isn't the powder at all but the bullet. My Browning 7-08 totally despises Hornady SST bullets yet loves the old Interlock ones in the same 139 gr wt.