Peaceful is the strongest form of diplomatic relation I believe. It overrides even murderous if I remember correctly.
This is incorrect. Murderous overrides all diplomatic settings.
However, it still has limitations. You cannot attack if you have already been declared a defender, and sometimes the process of declaring defenders can be a bit zealous.
Furthermore, murderous or not, combat or not, has no effect on whether you can
loot another realm. That is entirely determined by diplomatic status.
