I'm not sure if there has already been a video or discussion on the topic, if not it would make for a useful video at some stage, but what do you consider to be acceptable temperatures for GPU/CPU and at what temperature should we turning off our systems?

I ask because I have currently installed my tv tuner PCI card into my computer and it is blocking half of the graphics card fan (Sapphire ATI Radeon HD5770) as the graphics card covers up a PCI slot and only allows for space for one card