Since you're racing and running is timed, you don't really need a smart stop.
You need to make a short, timed run on the track and see what goes back into the lipo. Then you can figure a mah/min and have a better idea on where you'll be after 6 - 7 min. From what I've seen, this usually turns out to be numbers like 120-150mah/min so I don't see where you'll have a prob. But I'd find out rather than taking any chances.

Use the money for something else.