IIRC Itanium was faster on natively compiled HPC code, presumably because it had more FPUs and larger cache than the Pentium 4. But in general it probably wasn't a good upgrade and Intel would have had to sandbag x86 a lot to force Itanium adoption.

The other problem was that the Pentium 4 itself was kind of a dog, and then the Pentium M and Core lines started making that look bad, by which point the Itanic passengers could feel their socks getting wet and a growing concern about there not being enough life boats.