IPCs for 6502 or Z80 (4x "faster" clock but 3-6 cycles per machine cycle) processors were at the count of clock cycles per instruction
Even a measly 386/486 were much faster than that.
Enter the Pentium with the ability to execute 2 instructions in parallel.
IPC count were the big gainers recently as well
[1]: https://en.m.wikipedia.org/wiki/Wirth%27s_law