Well, the P3 lets you adjust it by voltage or wattage, though I don't know why anyone would prefer to use voltage, honestly... Either way, the two numbers are pretty much linked in the equation anyhow.
I believe that it has cutoffs based on amperage, to keep you from over-drawing your battery...or something. Just got the shipping notification that mine is on it's way back...hopefully they fixed it up. I've never really been a cloud chaser though, so I haven't really experimented with it. My DIY juice that I make vaporizes really nicely at about 8 watts.
Don't forget about the new eLeaf iStick 50Watt. I think that the new MVP also has some crazy high wattage limit...but, again...you'll have to be careful about rebuilding, some of them don't like to sub-ohm. Though at 50 watts, I'm sure that a 1.5 ohm coil will make just as much vapor as a 0.5 ohm coil.
(Quick Math on Dual Coils: 1 coil at 3 ohms fires at 3 ohms. 2 coils at 3 ohms fire at 1.5 ohms. 4 coils at 3 ohms should fire at 0.75 ohms. (Assuming that they're perfectly the same))