I use the 3.0 ohm CE2R4s in the MAP tank and the Mini at about 5-5.5 volts. Also like the 3.0 ohm smoktech cartomizers. The standard 2.6-2.8 work fantastic if you can drop down bellow 5 volts to about 4.8 or 4.7.
4.7 is the sweetspot for the 2.8 ohm ce2r4s.
Clouds of vapor has a decent selection, along with Madvapes. Madvapes is where I get my smoktech stuff from.