5s or 6s on the 1515 2.5d????

OK now that i keep my brushless stuff, i want to know what's is the best.
I've a Neu 1515 2.5d on order to put in my Mugen truggy. I want to know if i'am better to put it on 6s, spin it at 36630rpm and gear it with a 14T pinion to have a top speed of about 42m/h or i'am better to put it on 5s, spin it at 30525rpm and gear it with a 17T pinion to reach about the same speed.

Personaly, i thnk that put it on 6s and gear it down will place less load on the motor and draw less curent than on 5s with a bigger pinion, but i want to have your comments please before to order my pack.

I know that i ask lot of question, but i want to make the right choice, because a li-po in the $300.00 ++ it's o lot of money, so i want to choose the right one.

Ho! forgot to tell you that i'll make race only 95% of the time, and the other 5% will be yard bashing

Thank you

David