Old timers like you and me
used to think of the sweet spot in terms of
voltage. [I needed my 5V Prodigy V1 to get an intense hit from my standard 801 atomizer.] These days, I believe that
watts power is more useful. For many vapers, the sweet spot is 6-8 watts ... although each individual should discover his/her own sweet spot (e.g., perhaps yours is the 8.5 watts you mention).
And we can get there
numerous ways. The least expensive (unless you like box mods) is with an LR atomizer (e.g., Smok Tech Dual Coil or Boge 2.0) on a fat batt (or on the $35
NoEgo 18650 I just purchased). The most sophisticated is with that Darwin, which Chinner recommended. [BTW, Chinner,
thanks for the link!]