Questions about Revo G2R and 6s Lipo.

Hey, I've been on a break for this hobby about six months but now it is about time to start again... Originally I was waiting Mamba Monster Max, but It never arrived...

So, I have Revo with G2R with Singlespeed conversion and I have a few questions. I've been thinking to use 6s on Revo, Esc is going to be MGM and motor Lehner 1950/x or Neu 1515 x. But I cant deside whitch one and with how many windings. Is there going to be heat issues running 6s, or is 4s more sensible option? Another question is about gearing, is there going to be problems if the motors kv is 1200 or less? So can I find right pinion and spur so low kv motor that speed is ok. It woud be awesome if somebody could give me some advices...