I have a SL68P Cel 1.2 which can go up to 1.6GHz at default 1.5v. Prime95 stable, burnmx.exe not stable. Upping it to 1.6v didn't help. 1.65volts and Prime95 throws me a rounding error. Highly unusual.
It works perfectly at 1.537GHz/1.5v now.
Heatsink is Thermalright SK7 with a 30+CFM 80mm fan. Temps are 48C idle, 49C Prime95 (strange huh?), 52-53C burnmx. Either the mobo monitor is off or the IHS is making bad contact with the core.