KERSHAW DESIGNS E-maxx Dual 970-sized Motor Conversion Kit fits the old E-max and its only a $80 investment.
http://204.186.93.64/Dual970Conversion.htm

Hands down the simplest easiest conversion you can do and you keep the vehicle waterproof and these motors will definately hold up.

Keep the stock esc and with your batts you will have alota fun and shouldn't break much as far as the driveline with the increased power.

I can personally vouch for the quality and performance of the stuff from KD
ive used the 700-HO's and they where top notch.

If you where to go the brushless route you going to have to get an MMM or equivilent and prob want to swith out to Li-Po to get runtimes so that's around $300+$300= $600 at least once you add up 2 3s Li-Po's balancer charger esc motors ect not to mention upgrading the drive line.
Brushless will be hella faster and it would be and awesome truck but its also an expensive investment.