Clientpackets and Serverpackets, l2j and l2off use different coded Serverpackets so you will get different server packets from off, I never tested btw. About Clientpackets l2off reads them differently than l2j.
Dec? No we are not in 1950 to work and code in dec/bin, a hex F has a size of 16 bits, a FF hex 255, now what u would choose ? 255 characters of 0 1 or 2 characters of Hex?
Correct me if I'm wrong this is just personal experience.