There should be nothing you can do from using ordinary software that can cause any part of your Mac, including the graphics card, to suffer permanent damage.
That said, it is entirely possible that you have had a correlation between pushing your Mac to extremes and having it fail.
But there is no cause and effect.
Instead of generalities get down to specifics.
Some graphic cards have shipped with weak or bad fans.
The Mac Pro should but does not always kick the fans up early and fast enough, especially the GPU.
Running Windows? less control of the fans, Windows is not designed to work with the SMC and thermal sensors, but does better with GPU fan and cooling.
Software can be written that is not suitable for Hyperthreading, but those should by now be long gone, not that 10.5.8 was though, it was a disaster in 2009 and only fixed with 10.6.2+/.
In the past, and I don't have 10.8 or a 2009 model to use something to improve and boost the fans from their very slow fan speed, and allow you to manually kick them up a notch first and earlier: it is far easier to prevent and improve air flow and therefore cooling by doing so before it gets warm; much much harder to allow it to get hot and then try to cool.
HT and your processors are capable of jumps of 10-20*C in a flash, in the time needed to open an app or a document or other operations. So they can get warm, and it is possible for poor code to not allow a thread or core to "sleep" and go back into idle low power state - nag nag "are you free? are you busy? are you idle?"
Generally 85*C is stability threshold, hot, and you don't want to be there or stay there long.
What are you using to monitor temps? some are more reliable and accurate.
What are you doing if any to stress test? PRIME95 perhaps? Handbrake? Heaven? or just games and normal apps.
Then you can get to specifics if that was your intent, rather than generic and really impossible to answer otherwise.
Location. Air flow. Exhaust having a place to get pushed out and aware (so as not to recirculate hot air back into the front and inside the Mac Pro). Worst: putting a workstation in a closed area; a hutch.
And it is not unheard of for a few systems to ship with poor thermal pads or paste.
You can't over clock - the tools and access to firmware is lacking.
You should hear just how hot those MacBook laptops can get gaming, and how hard the fans have to run, or how hot the temps inside and on the graphics component, especially a couple of those with the highest end processor.
New disk drives are designed to save $$ by being able to run in warmer environments, same with servers, which is a big boon for farms and centers - many of which use the data center's heat to warm other areas and where 5*C warmer means less need for cost to cool. But cooler is always best. And an even temp rather than the stress of cold-hot-cold cycles which fatigues components.
Thanks for the replies.
I've been playing games on the Windows and the Mac side, most recently the the guild wars 2 Mac Beta. I also use Handbrake occasionally.
The reason I asked is I have been having trouble with my Cinema Display, flikering and eventualy going black. I took it for repair and it has been diagnosed with a faulty cable and is currently being repaired. During the intitial stages a faulty graphics card was suspected and I thought it may have been broken by being over stressed.
If the cable is replaced and all is well this is a bit hypothetical but the thoughts of having to replace the card had me thinking that perhaps you could cause this sort of damage.
The machine is currently under a desk with both the back and front open, the back has around 10" of space behind to wall.
The Mac OS X measures internal temperatures and boosts the fan speed based on those measurements. If it gets too hot, it Hardware will suddenly shut it down without warning. If the software crashes, the fans will revert to maximum (just as they do at startup).
There should be nothing you can do in regular software including games that does any permanent damage to your Mac.
The hatter wrote:
try for better air flow, boost the fans and when you are in Windows you would need to take extra steps, though the options for how to get system fans-- monitor them closely, use GPU tools, and to really monitor the system under Windows can't beat AIDA64 probably.
A thought and a question. Using smcFanControl proactively, I can set fan speeds for what I think will be the cooling load caused by what I do next. If I then reboot into Safe Mode, the fans speeds I set before the reboot are carried over into Safe Mode even though smcFanControl is no longer running.
I don't use Boot Camp for running Windows (Fusion 5 has too many features I need) so I can't test this but would rebooting into Boot Camp carry over any fan speed settings established before the reboot?