If something is memorable or famous, it’s historic – the sinking of the Titanic was historic, the passing of the recent health care bill in the U.S. was historic, the opening of the Khalifa Tower in Dubai was historic. But if something merely has something to do with the subject of history, or even if something is merely in the past, important or not, it’s historical.
Further is a distance that can’t be measured. But furthermore means “moreover,” or as Webster’s II New College Dictionary says, “beyond what has already been stated.”
Use percent only when a numeral is in front of it. Use percentage when no number is given.