Itanium was a RISC-y endeavour by Intel and it had it's problems but you can't really say it died because of x86_64. Microsoft adopted it and dropped IA-64 like a hot potato. Intel dropped Yamhill and other projects that attempted to bring IA-64 to the desktop as soon as they realized MS wanted x86-64. Performance didn't factor in because AMD would have never had the chance to provide the world all the CPUs it wanted (supply constraints)