I'd certainly agree that a cold battery gives less output, and leaving a battery unusued reduces it's effeciency until it has been charged to restore some of it.

I've just looked up the figures in the service manual, the starter motor is rated at 0.8kW, which if drawing 12v is about 67A (assuming 100% effeciency. Conveniently this works out at 1Hp !
The Starter itself however is rated at 180A

The Ten battery is 12v 8Ah which in THEORY gives enough power in ideal conditions and fully charged to run the starter for 2 minutes 15 seconds until completely flat (assuming a constant 180A current draw at 14v). As you say I would not expect this is practice, I'd probaly be happy with half that