I build my Kayfuns at 2mm-3mm id and 1-1.3ohms. With silica/ceramic wick I would lean to the 3mm side. I don't use ReadyxWick but I do use 3mm hollow core silica, In kayfuns. Gotta note if RxW works like silica, your are going to need to unbraided and fluff the wick into the well. Could just be me, but I cant get an intact cord to wick correctly.