There's always RISC-V.

Curious how Milk-V Mars CM [1] holds up to an eventual CM5

[1] https://milkv.io/mars-cm

A bit slower than a CM4, of course.

The Lichee Module 4A is a CM-style board, though not compatible with CM4, and is generally a bit faster than a Pi 4.

That's the fastest RISC-V you can get right now (but you can get 64 of those > Pi4 cores in one chip!). Chip and boards in RK3588 class coming next year, so that's ~Pi5.

A CPU instruction set architecture means nothing without someone designing, building, and shipping the rest of the computer around it. https://stat545.com/img/how-to-draw-an-own-imgur.jpg