4s or 5s lion or lipo

Ok guys, well I finally got the motor/esc for my 8th scale. I'll be running a feigao 7xl with a BK 9918 esc. Question is should I go 4s or 5s. For the time being I'll be running 12 cell nicd/nimh since I have them sitting around from when I used to race. I'm thinking of building a 4s2p lion pack using the emoli cells due to price. But I'm not set on it yet. I may end up going lipo and would like everyone's opinions. I'm not set on a 4s system, but I'm worried about the 9918 being able to handle the 7xl on 5s.

Thanks,
Pat