I have a new XPS 15 9530 with dedicated NVIDIA 750M graphics.
When playing a graphically intense game, such as Crysis, the graphics card warms up, and is then throttled. Looking at the temperature of the GPU, this is happening consistently at 75 degrees Celsius, which seems to me to be a low temperature to throttle at.
When this throttling happens the clock rates of the card are reduced to about a tenth of their normal value, making performance suffer severely, and games unplayable. The clock rates then return to their usual value after about a minute.
This is happening on both battery and AC.
I can find no settings relating to this in the NVIDIA control panel.