x800pro to x800xt

I bought a powercolor atix800pro to make my card from pro to xt I tried to reach the following clockspeeds core 526 and memory 573.I reach past the limit but my pc freezes.my card temperature is 38C on this speed and my voltage on this card is running at 1.4 and I am using latest ati drivers.I used ati tool latest version when I run it for less than one minute I get artifacts.
anyone know what I could have done wrong?

you might need to up the vcore with the pencil mod. My x800pro that I flashed to XT runs XT clocks at 1.4volts, but more than 530 on the core and it freezes. It should probably be stable if you pencil it enough to get 1.45-1.5 volts.

he did not mention it in his post but he has it penciled to 1.46v

i think the culprit is his power supply
it's called PoweUp or something and its max is 330 Watts

also, turning off fast writes may increase OC potential. Its found in the smartgart tab.

they are off
could his OC be to high, he has a P4 2.8 @ 3.5