The GPU is the biggest culprit for throttling in gaming laptops. Nvidia haven't released a number for the 970M's TDP, they say it's dependent on the game you are playing. It's generally accepted as being less than the 870M's TDP.
It also depends on stuff like the ambient temperature and air flow. I'm in the UK with an ambient room temperature of 21-22 degrees Celcius and I'm always fastidious about placing the laptop on a hard flat surface and making sure the vents are not obstructed. So far I've managed a 3hr Rome 2 session with the settings on extreme and saw no throttling. Likewise I've had a 2hr session with X-Plane 10 (which is a very GPU intensive app) and I saw my GPU temp climb to 85 degrees celcius, which is comfortably below the temperature at which it starts to throttle (over 90 I believe).
Having said that, I've no doubt with a synthetic stress test I probably could get this laptop to throttle, especially if I increased the ambient room temperature to over 25 degrees celcius.