That only applies if you want to run binary distros and applications such as Fedora or Ubuntu. If you're running a supercomputer and don't want to implement the

That only applies if you want to run binary distros and applications such as Fedora or Ubuntu. If you're running a supercomputer and don't want to implement the C extension then you can build your own kernel and programs. If you do that then anything from RV32IA and up can be used. You can also use a QEMU or Valgrind-like thing to JIT the C away. Or you can do what modern x86 does and annotate your cache lines the first time they are actually decoded instead of at cache fill time. That's just a little slower for cold code but the same for hot code. Having the C extension keeps 40% more of your code hot for any given cache size. There might be some implementation point at which Aarch64 wins by having bigger but fixed length code, but it's not at the low end and I don't think it's at the very high end either.