[adrian_b]

CPU ISA is at most a 2x difference for programs that use only the general-purpose registers and operations.

For applications that use vector or matrix operations and which may need some specific features, it is frequent to have a 4x to 10x better performance, or even more than this, when passing from a badly-designed ISA to a well-designed ISA, e.g. from Intel AVX to Intel AVX-512.

Moreover, there are ISAs that are guilty of various blunders, which lower the performance many times. For instance, if an ISA does not have rotation instructions, an application whose performance depends a lot on such operations may run up to 3x slower than on an ISA with rotation instructions

Even greater slow-downs happen on ISAs that lack good means for detecting various errors, e.g. when running on RISC-V a program that must be reliable, so it has to check for integer overflows.