Well, its hard to determine exactly how long batteries will last, I know the formula used is:
Duration= 60*(capacity/mAH) /amp draw of the motor.
I believe a stock stage one motor draws roughly 1 amp draw at full throttle running on 4.8v.
So an example would be 60*.75 (750 mAH)/1=45 minutes run time.
At 1000mAH your run time should be 60 minutes, assuming that they use the same voltage. If its higher, the motor will draw more amperage. Stock FETs can handle up to 3.5A, while the stock motor can handle up to 8.4A I believe. This is why most people stack fets and go lipo or something similar.
The user Action B has a very cheap FET stacking service, and is an approved provider.
http://www.xmodsource.com/forum/show...061#post253061
Disclaimer: I doubt anyone has ever seen those run times out of radio shack batteries, I am just providing the formula used for larger scale RC; I can only assume its similar for Xmods.