Something you have probably already figured out: ask 10 (or 100) bench shooters on how to tune a 6PPC and you'll get 200 answers. That is why it is a competitive sport. The joy is finding what works, the agony is not finding it until after the last target of the weekend.
Because I can't help it, here is my advice to you:
Number 1
The biggest thought process you need to get over right now is believing that you can find a "perfect" or even "good" load and stick with it -- that will only work if you are happy averaging in the '3s. To shoot consistently in the twos and smaller throughout any day, you have to make small adjustments -- call them micro-tune changes -- to get the gun to its razor-edge best. The goal is to learn what kinds of things cause variation, and how to respond to keep the gun on that edge.
Every top shooter has his own recipe of changes that he goes to as he sees changes in the target or feels changes in the conditions: powders and amounts, seating depth, and neck tension are the common ones, but far from the only options. The PPC is generally accepted as the most accurate cartridge in the world, or we would be shooting something else. But it has that reputation because it responds predictably and measurably to the small tuning changes, not because it doesn't need them.
The top shooter at the Nationals last year shot five different loads on the last five targets to win. Not a lot different, but if he hadn't been making adjustments, he probably would not have gotten the full potential out the gun. That is why an forum discussion of seating depth to 4 decimal places is simply the wrong way to approach your rifle. Much better to approach it as "as temperature does up increase (or decrease) (seating depth/powder charge)" or "holdoffs for the left wind are more predictable than the right wind on this range". These kinds of learning that will lead you shooting small and knowing why. Shooting small involves a very dynamic system and laughs at absolutes like case length, .258 bushings or 28.4 grains of PerfektPowder, even when the conditions you can measure seem the same. Adjust. Adjust. Adjust.
Number 2
Find some local competitions and get in them. As much fun as it is to shoot a small group, it is even more fun to know it is actually SMALL. Sometimes a .3 or even a .4 is really small at 100, sometimes it is big at 200. One real-world way to tell is to be side-by-side with other shooters and see what they are doing. A guy running a top-fuel dragster all by himself can post great times, but still have a dog of a car. Don't worry about the winning, beating other shooters, coming in last, or any of that horse-pucky. Competing is about learning, not winning. One weekend of competition will teach you more than 5000 rounds on the practice range. You will overhear a hundred tips that help you understand your gun and its capabilities. And some of the people around you will be genuinely friendly and actually desire to help you make that gun work. When you shoot your first match, your first small group, your first agg in the 2s, your first yardage top-10 you will be ecstatic. BR competition is not about beating someone else, it is about putting a framework around the reason you like to shoot small groups and being able to quantitatively measure your progress against yourself, not anyone else.
Number 3
There are two reasons for going to the range: first is tuning and second is practicing. To do either, you need to be able to make those adjustments I mentioned earlier. Take your flags and take enough equipment to load at your bench on those days. You need to be able to adjust something while you are shooting. The smart strategy is to adjust one thing at a time and pre-loading at home seriously limits the variety of things you can test. Take Notes. The best days in practice or competition are when you see something, make an adjustment on the fly, and it works. That is a sign that some of the learning is working.
Number 4
Find a mentor -- preferably a good, active competitor, and learn his system. This is not an armchair sport. It is not learned by averaging the comments of forum posters, mediocre performers, or listening to 20 pieces of advice from 20 sources. Good shooters each have their methods for analyzing results and adjusting, but those methods are not mix-and-match... pick one guy to help you and ignore the rest until he can't teach you any more.
Rod