My thought process is, once the gun is in hand and the target game decided, I ask myself what is the limiting factor on this setup. Is it the rifle, or is it the brass? If it's a strong modern bolt action or single shot, then the brass is the concern, and monitor the brass most closely for long life. The chrono and reference books are useful tools, but again, I've seen brass fail in cases where the book and the chrono said it was a good load. You also have to consider the bullet. You could safely launch a .30-30 bullet out of a .300 RUM 1000 fps faster than its design velocity, but obviously, it's not going to perform properly.
Perhaps someday I'll obtain a pressure measuring gizmo, to add to the toolbox. If the action is old or of lesser strength, then the brass may not the limiting factor in load development.
To me the craft of handloading is one of making high quality ammo, that accurately launches projectiles appropriate to the task. The ammo should safely utilize the full potential of the gun, while still keeping an appropriate safety margin. To those ends I'm going to use judgement, and a variety of tools.
