The Z80 was not much slower than the 6502 (2x slower at the same clock speed if you factor in the more complex operations). The limitations of the spectrum were

The Z80 was not much slower than the 6502 (2x slower at the same clock speed if you factor in the more complex operations). The limitations of the spectrum were not related to the CPU itself, but the fact the CPU had to do everything, and even this way the raw hardware capabilities were shit.