I just ran the Find Max... tests in ATITools on my BFG 8800GTS 640MB. I only learnt about the tool today so I have no idea how reliable it is so I was hoping someone could help me interpret the results.

For the Find Max Core test I got up to 636 before my computer crashed and restarted itself. The temperature was up to 81C.

With the Find Max Mem test when I got to around 1030 artifacts began to appear (Although the tool wasn't actually recording them). As a result I just ended the test, but the temperature was at 80C.

I ask for two reasons, first and foremost because I don't know how trustworthy the tool is, and secondly, if the results are reliable, I don't know how much lower then the max I should set it.

I presume the temperatures are fine (though I have heard a wide variety of different claims for what is the max safe temperature for the card)?

Overclock manually. These cards handle 90s good. 100C i've heard is throttling point

Yes, overclock manually...these cards are fine even into the 90 degree range. Don't worry much unless your card is remaining in the upper 90's or higher for an extended period of time. In my experience so far, I have not been able to exceed these safe temperatures without experiencing a crash before hand. In other words, cards these days typically safeguard themselves, but you should still check occasionally. Overclock until you start seeing artifacts in games, then reduce speeds slightly. Also, a more gpu intense game that utilizes more parts of the card at any one given time will probably heat up your card more than an older game will.