I run 12mg in all my tanks (Kayfun, RSST, and Protank) and 6mg in my RDA's. For RDA's, running 12 gives you so much throat hit and nic that I can no longer enjoy the vape. For a warm vape, you definitely need a high wattage device, something that goes over 20 watts. Whether that's a DNA style regulated device or a sub ohm build on a mech, that's up to the end user and what appeals to you.
I just recently got a Cloupor DNA clone, which I vape a 1.3 ohm coil at 24 watts on a single cool Magma. It's just warm enough for my tastes. I can achieve the same vape with a .27 ohm build using a fresh battery in my mech.