Yeah Efest 18350 are only 10 amp but at .8 fully charged @ 4.2 volts he'll get 22.05 watts and run an amp load of 5.25 amps so he's safe there but I wouldn't go any lower than a .6 coil as after firing a coil the ohm can fluctuate some and at a .6 you are @ 7 amps which means you are very close to the battery amp capacity.
I generally only run 3/4 of the continuous amp drain capacity of a cell for a safety precaution. Now we aren't going to hold the button on a mech mod until the battery goes dead, we technically are only pulsing the battery when vaping. So for instance a Sony VTC5 is rated 30a continuous 150a pulse so could you safely vape a 40a build according to the pulse rating yes in theory, but is it worth testing the theory not in my eyes it isn't and if that build were held continuously it would surely vent the battery and end in catastrophic failure.