What is the max safe temperature for a nimh battery???

I have a old school rustler that I have novak 4.5R gtb system in, I use a 8 cell gp3300 nimh battery with and my batteries are getting pretty hot around 160F, if I drain the pack to where the truck gets pretty darn slow I see temps on my battery around 180F.

Is 160F to 180F too hot for a nimh battery, I have run this battery a couple times like this and it seems to be doing allright. If its too hot I will just gear down a tooth or two on the pinion.

I know someone is going to say that your not supposed to run the novak gtb brushless stuff past 6 cells but I have been running a 7 cell pack with this setup for a year. Even with the 8 cells being run the GTB esc only gets to about 115F to 120F max, and the motor stays around 120F to 130F and the darn thing runs great and screams.