I use around 0.2-0.3 with 24Gauge 2.0-2.5mm coils for my mech mod. I find anything 0.5 or higher just takes too long to heat up. Anything 0.5 or higher I just vape on my vv/vw devices.
For my 40w VV/VW box mods i just build anything 0.2-0.7ohms, build doesn't really matter as much as RDA/Airflow for vapor production in vv/vw mods because you can adjust watts/volts, at least from my experience, im sure there are others who will disagree. I like
vaping at 0.2-0.3 most of the time though, I might grab me a sigelei 100-150w just to see how the vape is at higher than 40W with 0.7ohm+ coils.