Twin Force Brushless Questions

Ok, i've decided to try and set my truck up for maximum runtime and 30-40mph.

So I will copy this guy here who setup a lipomaxx :)
http://www.kmcsonline.com/casemod/emaxx/
(He may be a member here?, remember seeing the name )

He is running a lehner basic 1600xl, warrior 9920 and 6s lipo cells.( ~24 v)

I was wondering if stepping up to a lehner 19xx or 22xx would help me increase my runtime even further. I had read an article where somebody said that these motors will run at lower amps for the same power output.

Do you think this is worth it, or just stick with the 1600?

Either way i'll be getting the following:
Airtronics MX3 Radio
Hitec 645 or JR650 servo
Warrior 9920
(3s2p LiPoly 4200 or 6300mah) x 2 for ~24v
AstroFlight 109 charger