"Its not so much a case of me wanting to load to the max, but i have a 5.2 grain variation between max loads and i want to know the true max load to keep things below that. I guess the safest bet is to take the sierra max load and keep my reloads below that, what do you think,..."
Stan, the problem is that reloading is not an exact science. We are working with an organic compound, powder, that gives us some unavoidable inconsistances. Thus, what's "max" for me may be less than for you, what's max for you may be less than someone elses max. THAT'S why the manuals max loads vary and why they ALWAYS say to start low and only work up if no pressue signs are evident!
In other words, the starting loads in a book are most important because they do give you a safe starting place. After that, what becomes critical is how YOUR RIFLE digests your loads as you increase charges. Understanding this will help you recognise that the source of the data doesn't much matter, powder maker, bullet maker, new, old, etc., you simply MUST learn to recognise the signs of over pressure.
In time, a few years perhaps, you will become comfortable with loading and gain enough experience to recognise when you may increase your velocity, but NOT NOW! For now, it is safest if you stop at the most conservative book's max load, not the most generous nor an average of them.