Hi I recently had an issue with a graphics card and needed to know some details about how they work to avoid another accident...

I have a mid 2008 macbook pro 17inch, 2.6ghz, 4g ram, with a NVIDIA GeForce 8600M GT card.

So I was playing Starcraft II and I usually keep an eye on temperatures, honestly not knowing what is good or bad but just so that I can monitor if its unusually high. The CPU is consistently 165-170 and the GPU at 170-185 (Fahrenheit). It was sitting around 180 during gameplay and the screen went all funny with random lines and pixels and stuff. I remember reading about a batch of NVIDIA cards (that happened to apply to my macbook) and they used a lead based solder, which to my understanding allows it to melt at a lower temperature, so I figured it overheated and separated from the logic board. Took it in and it was just that, replaced it under applecare, done.

SO... my question is (cause it's more than likely they just put in another non-updated version of the same card) what is good and bad temperatures for graphics cards, how to avoid overheating, etc.

I also plan on upgrading to a 27inch iMac with the highest available card in it this summer after (when I hope) they refresh them. Good idea or bad idea? Better alternatives?