Need advice on a setup?

[mkrusedc]

I have an E-Maxx with all appropriate drive train upgrades. Mostly RPM plastic to keep my weight down. I purchased a Neu/1y/1f motor and tried to use it to with my existing MM and 14 cells. The voltage was too high. I do have two TrackPower 2s1p packs that I have not opened yet, but could probably use with the MM. I plan on purchasing either a MGM 224/18 or a 160/18 because I can not tolerate the cogging.

My question is should I open and use the TrackPower batteries or because the MGM can handle more get a 6s or 18 cell batteries? My current gearing is 52/17. I wanted at about 40mph for bashing. The bigger batts according to Brians speed calculator put me abouve 50mph. If I went with the bigger batts I could get a heavier extended chassis for better control or smaller batts and stay plastic?