I decided to rebuild my Lemo again in the hope of getting similar performance to the Billow, this time went for a dual coil of 26g kanthal and came out to 0.4ohms. The first few hits were great but I noticed it wasn't wicking properly again - I'd use quite a lot of cotton but I'd left the channels free and it just didn't seem to be wicking at all, no air bubbles were coming up. So I googled and found this on reddit:
"it also seems to get vapor locked. after filling it, i tend to have to carefully hold the glass down then undo the top just enough that an air bubble comes up. once the correct pressure is set (2 or 3 bubbles after 4 or 6 hits) it seems to correct the wicking issues."
So I gave that a try, held the glass down in place and slightly unscrewed the top, an air bubble came up so I tightened it up again, and then 6 or so more air bubbles followed! Now it's wicking perfectly, running it at 50W with no dry hits - think I'll be retiring the Billow after the next tank is empty, it started leaking again without me changing anything from when it wasn't working at all, too annoying. Lemo wins!
Edit: I'll probably keep playing with the Billow actually and hopefully I'll be able to master the wicking to stop the leaks, but now that I've got the Lemo performing similarly I'd say it's much better overall.