Motor + batterie setup for crt.5

I'am to order a new motor and li-po for my crt.5.
I want to know if i'am better to take a high Kv motor like a feigao 540s (in 4500 to 5000Kv)on 7.4 volts maxamps 8000mAh or take a lower Kv like feigao 540 10L or 11L on 14.8 volts maxamps 4000mAh.
I've the UBEC.

I want a powerfull system (in the 40 m/h range) and long runtime. And i plan tu put 2.2 truck tire on the crt.5 insteed of the buggy tire.

Thank you

David