I'm guessing you are running the 5000mAh pack from Losi.

I can't predict a race environment since I haven't raced since starting lipo. I do get at least 20 min with a GTB and 5.5 in bashing circumstances however. Mix between grass, asphalt and dirt with a T4 with minimal jumping and a lot of full throttle. There are some threads about 20 min offroad around, check them out and see what they are using. A cutoff/warning would not hurt to have however.