It is not optimal to use 8-byte integers instead of 4-bytes.
CPU works just as fast with both, however your CPU cache is limited and you'll put more 4-byte integers into your L1.
I don't really understand what you want to convey. CPU is very fast with any kind of integer size. There's no performance penalty to use 1-byte integer compared to 8-byte integer. And there's performance penalty when your L1 or L2 or L3 cache is busted and you need to go to the next memory layer.
1-byte integers or any other integers smaller than 8 bytes (64 bits) save space only when they are parts of arrays or structures.
As individual variables, they take exactly the same space as 64-bit integers, both in registers and in memory (i.e. in the stack used for automatic variables or in the heap used for dynamically-allocated variables), because of the alignment requirements.
Therefore it never makes sense to use other integers than 64-bit, except as members of aggregate data types.
A database table is an aggregate data type, so the use of small integers in some columns may be justified, but such types shall not be used for variables in the programs that process data from the tables, where misuse of the small integers may cause overflows and there is no advantage from using smaller integer sizes.
