Moving this over to Regulated Devices...
I use an Arctic with 0.2 coils on my iStick 50, runnning maxed out all the time at 45-50 watts. It'll fire down to 0.2 no problem.
The Subtank only has 0.5 and 1.2 pre-built coils, you could potentially build lower with the RDA attachment but I don't know that I would, at least without filing out the liquid holes a bit. You can get a little better vape and more power before you get dry hits by taking a needle and gently making a couple impressions on each side of the factory coils at the liquid ports, but general consensus is that other tanks like the Arctic, Starre, Herakles and High Voltage all deliver a bigger cloud - though even maxing out the iStick at 50 watts you're only getting a taste of what they can do...