Yep. The Amstrad CPC was an effective 3.3MHz. Most 8-bit machines of the early 80s had reasonably comparable CPU performance: the real speed differentiators were the graphics hardware (Spectrum fast because you had so few colour bytes to write, CPC slow - until you learned how to scroll with the CRTC) and, if you used it, the efficiency of the BASIC/firmware.

There was a 16MHz Z80: Amstrad briefly built a machine on it in the 1990s (the PcW16).

TI still sells 15Mhz Z80s in their TI84 graphing calculators.

And still charges what they cost in the 80s

I'm kind of wondering why there isn't an open hardware calculator yet. Given the mark-up most of these brands have, it might actually be viable.

The ACT and SAT require certified calculators

Well, I imagine we could get citizen funding for that.

EDIT: Oh, the certificate is with the product? Well, there might be some smaller players who currently can't compete with TI who could handle the production side.

Hardware-wise it should definitely be easy enough to create a cheaper calculator just as capable of meeting the requirements, no?

Why do people still buy the TI-84? I used a TI NSpire when I was in school and it cost about the same

That's a little unfair, the BBC Micro ran at 2 MHz and was released before the Spectrum.

It's not wrong though, the 6502 was much slower clocked that equivalent contemporaries.

However IIRC most contemporary architectures were closer to the Z80, so the 6502 was considered impressive because it was competitive despite a much lower clock rate.

1 MHz clock on the 6800 family of processors, including the 6502, is equivalent to 2 MHz clock on the Z80. The 6800 architecture used a so called two-phase clock. Each phase, positive and negative, of the clock cycle was used to do work.

I would suggest it is between 2 and 3 times, but it depends on what kind of code you are running.

A 2 MHz 6502 is approximately equivalent to a 6 MHz Z80, give or take 1 MHz depending on what you're doing.