In a 5 min race, there ahsouldn't be any prob. You're prob using less than 200mah/minute as a guess. Check what goes back into your lipo on teh chareger and see what kind of mah/minute you get. Then you can know for sure what kind of time you're safe running.

The low voltage cutoff is just a setting in the esc. Once activated, it will interrupt power when lipo voltage falls to a set value. I don't know what that cutoff is set at, but default values are usually around 3v/cell so a 2S would hit the LVC at 6volts. As long as you're above that value, everything is normal. The actual voltage value may be adjustable as well. If the esc has profiles, the lvc, if activated, should be active across all profiles except one for NiMh. If you run NiMh, you run with no cutoff since voltage varies and there is really no minimum voltage for NiMh.