More than 140mcg/day would probably give diminishing returns... your schedule of 120/day in 3 dosages isn't bad, but with 6 tabs/day, and assuming you're awake for 18hr/day (I know that's usually my schedule), you could take one every 3h and have a more even blood level.
Or, base it on a 12h waking period, and take one every 2h... I used to take one every hour for 7 hours, starting at 9am; was done dosing by 3, which meant I could sleep at night. Saw great results too...
-M