A good starting point would be a coil at 0.4 to 0.45 ohms with a single spaced coil. Ohms law will tell you that a 0.4ohm coil at 4.2v will get you 44 watts, but there will a small amount of voltage drop before it hits your coil (from whatever wires, metal, and connections the current is flowing through), and there be some voltage sag as the current is drawn from the battery, so it may be around 3.9v at best (giving 38 watts) to start with, and then fall from there as battery voltage goes down.
A clapton coil can require a bit more ramp up (and ramp down), and you don't have any power curves to play with to give you an initial boost, so you might want to build a smidgen lower with claptons to get what you are looking for in a
vape (but maybe not). Now, voltage sag of the battery is directly related to the current draw, so the lower you build to get higher watts, the more voltage sag you get, reducing your watts and can be like chasing your tail. But your power range is nowhere near extreme, so you should find something that works well pretty easily.
Sorry to be so long winded ... I'll go back to snarky little remarks now
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