.6 Pocket X in the Naulilus X, and the standard Aspire .7s in the Nautilus 2, at the moment. I have a Zenith tank coming soon...so I'll see if noticed any difference with that one.
I am not too familiar with those tanks or coils, although both are from well know manufacturers, shame about the coil fails. Have a try at making your own coils. Not too bad to do and lots of guides online. Your own wire and cotton could make a difference.