Here is what I learned saturday after racing my D8-E for the first time. With my MMM with a 2650KV castle motor and a 4s SMC 5000 40c lipo on a track with 2 huge straights (34 sec avg. laptimes) I went the entire 15 minute main, about 3/4 of the way on the last lap my battery hit cut-off but I made it home just fine. I was not full throttle on the straights every lap but only when going for a pass.
I am sure with a lower discharge rated battery I could have gone the entire 15 minutes no problem or maybe a smaller track also.
Hop that helps you out any.