My SAPPHIREX800GTO2 DUAL DVI CAME WITH THE BIOS SAYING IT WAS R430 12 PIPES, BUT I TOOK IT APART CLEANED IT AND IT WAS R480,THIS WAS WHILE I HAD IT APART TO PUT ATI 5 SILENCER ON IT. ANYWAY,540 ON MY GPU IS A BIT UNSTABLE.530 IS OK,610 IS MAX STABLE ON MY MEM.I FLASHED IT TO XTPE AND USED RABBITT TO LOWER THE GPU CLOCK A LITTLE. I RECOMEND ZALMAN FANS OVER ac ATI SILENCER.IVE HAD BOTH MY X800'S FOR ABOUT A YEAR AND THE ZALMAN STILL COOLS LIKE DAY 1. THE AC ATI SILENCER 5 REV. 2 RUNS MY CARD HOT AROUND 73DEG. USED TO COOL IT 42 UNDER EXTREME LOAD. IT JUST WORE OUT I THINK.
If I would you I would flash it with X850XT but not X850XT PE. The X850XT (520/540MHz in most cases allows better overclockability than X850XT PE BIOS or will voltmod the core to handle stable 540MHz.