Use steamengine!!!!!!! What kind of vape do you want from the coil? Do you want to run them at 30 Watts or less, try some 28 wrapped with 38 or 40 awg. You want more wattage try 26 or 24 wrapped with 32 or 30. You want alot of watt say 100 or more try some 22or 20 in the core or double-up on the cores with the smaller wires.
All can be done at .5ohms with claptons. Of course it get harder to do the thicker the wire(s) get. Why do you think you are limited to .5ohms????? You could probably do as well with more or less ohms.. I would be targeting vape quality, surface area, heat flux and heat capacity..... Let the ohms and watts fall where they may, to provide the others.