have u checked the temp of processor. check the case fans and CPU fan as well..
Get your power supply tested
I'll probably take the PSU to EGS next week to have it tested.
Dont bring only the PSU, pl bring you full CPU, i know it may be a hard work but we need it to test.
if ur vga give color strips while it's hot, the VRAMs getting low voltage or low amperage. poor quality caps exposed to high temps usually cause dat, or PSU not providing sufficient amperage will behave the same.
OK here's another thing I found out. Setting the power limit of my GPU to minimum seems to get rid of the crashes. I did some gaming for a couple of hours this way and no crashes so far.