I swapped to a 20700 mod about a month ago...and man am I glad I did.  I kill 18650s...they'll still take a charge, but they only last a couple of hours after a week or so.  I've been running 2 sets of 20700s for a month now, and a fully charged set is still holding up all day, 0.17 ohms and 80w.

The mod I got comes with adapter sleeves so I can still use 18650s in a pinch, which came in handy when power was out for a couple of days this weekend, so having a 20700 mod is a win/win in my book.

The mod I'm using is a Reuleaux RX2 20700.

Any other 20700 converts out there?

I've been thinking about getting a single battery one.  I just switched to the Fireluke tank with the mesh coil ( man it has good flavor ) but at 50w it goes through a 18650 pretty damn quick.  I hate swapping out batteries in the middle of the day.