New AGP Sapphire X800GTO (R480 core, 256MB ram, 12 pp) with AC SIlencer 5 installed on a SIS M871G rev 1.5c mobo, 1 gig corsair valuselect RAM, WD 80G SATA HDD, Aspire QPack case w/ 420W PSU, WinXP Pro SP2. Running ATITool 0.24 to find max core with RAM @ default (490MHz). Tool runs up core clock to 545MHz fine, no artifacts detected, then crashes at around 545Mhz. The RAM OC detects artifacts around 610Mhz with the core a default (400Mhz) and doesn't crash. GPU temps are staying at or below 55 C according to ATITool the entire time (Arctic Cooling ROCKS! ) I haven't had this occur previously with the ATITool with my other card, though this is the first try at OC for this card. Any ideas as to what is happening with the core OC that causes the crash?