Too many variables in your question to give you a valid answer. One would need to use a pressure barrel and measure each load to have any kind of accuracy. "+P" is a pressure issue, which can be changed drastically by changing the cartridge overall length. Powder is only one of the factors. Case capacity affects pressure, and even that varies between cases from the same manufacturer in the same lots. Most, if not all, loading manuals will indicate pressure for each load they list. That would be the best place to begin to find the answers you are looking for. Bullets (or "boolits", sigh ) also vary in weight and shape and will impact pressure levels. It's not just a matter of increasing the powder to make something +P. Check the manuals.