By all accounts I can find Itanium performance was good, perhaps even great when writing assembly. It seems to reinforce the point that ISA doesn't really matter.

But let's be clear: Of course ISA matters. It's just as trivial to make a bad ISA as it is a bad syntax. But does the ISA of modern superscalar processors matter? Probably a bit, but certainly not a whole lot.

It wasn't good vs peer competitors at the time (HP-PA, DEC Alpha, IBM RS/6000, even MIPS). And it was very expensive. Huge die. It was an expensive, strange thing, that didn't have the necessary 2X peer performance advantage to offset those issues.