at what temperature should i be seeing artifacts for a 8800GT?

hey i bought some superclocked XFX version of the 8800GT(670/1650/975) about a month ago. i have been extremelysurprised and impressed so far. like most 8800GTs, it was crashing a ton untill i raised the fan speeds to 75% (stock is 25% for some reason). now that i have raised the fan speeds, im running into a lot less problems.

anyways. every now and then (happened at least twice a day over weekend) i see artifacts and have to turn comp off by holding down power button. i dont expect perfect, but is this out of the ordinary or something?

at desktop, riva tuner says im getting 46 C constantly. i played crysis (max, 1280x800, no aa/af)for 22 minutes and the temperature stayed at 64 C most of the time, occasionally bouncing to 65 and very few times 66 before going back down as i shut down game.

this is my first time looking at temps, so i dont know what they were at most of the weekend. granted, i was playing a lot of games this weekend, but should i be seeing artifacts every now and then if my temps are for the most part this low?

well it didnt artifact at 64 C (at least im not sure). i tested it today for about 20 mins and it worked fine.

like i said it only happens when im doing a lot of gaming (weekends lol). im just gonna leave my GPU temp monitor up always now (second monitor off to side, not for gaming)

by artifacts i mean i start seeing artifacts on the screen. kind of hard to explain, but you know when you see them. mine pretty much look like small green squares all over the screen.