Why does my video card crash with out artifacting?

[titanmiller]

If I push the core on my GF4 Ti4400 above 305 or so it just locks up and displays a single frame until I do a hard restart. I have never seen core clock related artifacts.

 

[KillaBong]

My ti4600 does the same thing after about 330 mhz. I think its just overheating and crashing, because it lasts a lot longer at higher speeds when it hasn't been on. I would assume artifacting is more related to it making errors at that speed, and locking up is heat related.