Performance question: 4 versions of same sketch

AWOL:

The surprise for me was how poor the 64 bit version performs, and its size.

On an eight bit processor, that's a surprise?

Well, the 16 bit version is faster than the 8 bit, on an eight bit processor, so its not that simple. The 32 bit is about the same speed as the 16 bit.

So there are multiple factors affecting the speed, and program size. Some factors improve the speed with increasing variable size, other factors have the opposite effect. I'd just like to understand them better.