That depends on if you like a warmer vape or a cold vape. I like a warmer vape and with a 3.0 ohm carto, I would set it around 4.4 - 5.0 volts.
wv2win....respected veteran of the forums....
The Beauty of vaping..... were all a bit different.
I use 3.2 cartos, single coil and I vape 40/60...mostly clear fruits and such. I always start at 3.4 on my Provari and stay there a while....then bump it one or two tenths at a time. Usually never go obver 3.9 volts. It really has alot to do with your juice and what flavor/flavors is in it and the VG/PG mix.
We are all so different. But there is one constant........as your bumping up the volts.....and hit the "burnt taste", back it down a couple tenths of a Volt. Thats probably your sweet spot.
I stay at the lowest voltage I can and still get a good taste out of it. I dont care if my vape is warm or cold myself, I just want the best "Taste". I think it could be in my mind also. I sometimes think that if I can vape at a lower voltage, I can keep a Cartoi in service longer. This may or may not be true at all....its just something I have lead myself to beleive.
We all a bit different.