MMM and Xray 808

[nl12]

I am gonna get a MMM and a Xray 808, I am having major trouble figuring out what I want for motor and battery, I know I want Neu motor and Neu 30c lipos. I want to gear it for approximately 50mph, I want it to accelerate like a 1/18th on 4s if you know what I mean. I am not sure if I should do a big motor like 1515 or 1521 and a 5000mah pack, or a small motor and shoot for a sub 7 pound buggy with a 1509 or 1512 and 6s 2500mah or 3s 5000mah, or is there a better combo to make this a super quick buggy? I am just going to bash this thing most likely. Help me build something sick.
Thanks