Nimh battery question

[toolmakerman48]

does anyone know why i am getting better performance out of a 7.2v over a 8.4v battery pack. not only am i getting longer run times but better performance. I thought that more volts meant faster. heres the batterys

http://www.all-battery.com/tenergyp...ratenimhbatterypackswithtamiyaconnectors.aspx
http://www.all-battery.com/84v3800mahhumpTraxxas11313.aspx

the 7.2 v tenergy is almost comparable to my lipo in the begining but the 8.4 is runs the car hot and slow

 

[hamz9561]

The 7.2 pack can put out more current than the 8.4 (40 Amp vs. 38 Amp). The 7.2v also has more capacity than the 8.4v (4200 mAh vs. 3800 mAh). The current out is like how much water you can send through garden hose (Amps). The capacity, listed as Milli-Amp Hours (mAh), refers to how much of a charge that the batteries hold. Think of it like a gas tank in a car. The more mAh the longer that the truck can run.

 

[toolmakerman48]

where does volts come into play then? because at only 2 amps more and 1.2 volts less wouldnt the 7.2 be at a dissadvantage?