> Maybe a little advantage can be, if 64-bit code runs faster than
> 32-code on 64-bit CPUs, but I am not sure if it is true.

64-bit code runs slower on a 64/32-bit Power(PC) CPU in 64-bit mode than 32-bit code runs on the same CPU in 32-bit mode. In fact, this is true for any ISA where 32-bit and 64-bit instructions only differ in width (i.e not for x86(-64) or ARM).

> G5s […] can execute 32-bit instructions and have support for 32-bit OS.

Indeed, that's why MorphOS can run on G5. The same is obviously true for the X5000's e5500 core, which is why MorphOS and OS4 can run on it. The only 64-bit-only Power(PC) I'm aware of is the A2.

[ Edited by Andreas_Wolf 06.06.2022 - 17:57 ]