Its not uncommon for 550 to outperform other powders neat the same burn rate. H100 is a little slower, as you have discovered, and may get close to the same velocity if you reach the same pressure. I try to stay below extractors marks of any kind with my final load, but its good to know where they start to occur. The extractor mark, in and of itself, does not affect accuracy, but normally accuracy will be less at high pressure. (not always) I would go with the one that shoots the best in a ladder test if I were you.