How much Caffeine is Just Too Much?

know you would have to drink a ridiculously large amount to actually overdose, but how much is just too much? On weekdays , I normally drink about 500-700 mg of caffeine ( 8 oz of coffee=100 mg roughly)spread throughout about 18 hours. On the weekends I drink absolutely none. So I know I'm nto actually addicted because I don't get headaches or anything when I don't drink it. I do get more sluggish, and don't have that extra edge