Being a long time vaper, I can tell you that you will not get 6000Mah out of an 18650. maybe 3500, but that’s it.
There was a thing a few years ago with a dump of Chinese batteries that were said to be 6000Mah, even some that said they were 9000. but when you actually used them, they would be lucky to be 1500 to 2000. It is best to stick with the LG’s or Sanyo’s (3000 to 3500 Mah, High drain) which are fine if you are buying a few at a time. Just keep that in mind when you get these. Also, if you don’t already have one, get a Nicore charger or a RC Charge controller so you can actually test your batteries and find out exactly what they will hold.