It's all about the resistance of your coil. You are right, IMHO, that a good vape, good flavor and good vapor, is gotten somewhere around 3.3 to 3.9 volts. Maybe on the odd chance you are using a thinner e-liquid or a great wicking wick you might be able to get over 4 volts.
Otherwise all you get is a HOT vape and a burnt taste and throat.
I have run my Provari up to 4.5 volts with a 1.4 ohm coil but only for one or two draws. Then it is back down to my normal 3.4 to 3.6 volts.
If I use a slightly high ohm coil, 1.8+, then I might make it over that 4 volt setting. But I still find the best vape is around the 3.5+/- volt setting.
If you do the math, Ohms Law, for the wattage you are using on a regular resistance coil, 1.3 to 2.2 ohms, you will be somewhere in the 7.5 to 11 (Maybe 12+) watts.
But if you lower the resistance to below 1 ohm then the wattage goes UP for the same voltage that you are using.
If you used a .5 ohm coil at that same 3.6 volts the wattage would be 25.92 watts. If you bumped the voltage up to 3.9 then it would be 30.42.
If you lowered the resistance down to something like .35 then you would have 37 watts for that same 3.6 volts and 43.45 watts for 3.9 volts.
In my opinion all this hype of higher wattage devices is just that HYPE and of course the show offs that Cloud Chase.
There is a Rip Tripper video about the Gi 2 box mod that does 100 watts. He was vaping a .3 ohm coil at 45 watts. That equates to 3.67 volts. He did bump it up to 75 watts and then coughed his lungs out after taking a vape.
There are some that vape at higher voltages but they only do that for a short period of time to get the most CLOUD they can.