I am quite not sure about what is the question..
If this is your Q
"But the tablespace SYSTEM has an extent size of 64KB.
Is this good? Isn't it better to have a 256K extent size in this case?"
Then i did ans, it immaterial as long as you have all segments defined the storage & it depends on those Extent size not TS.
funky...
"I Dont Want To Follow A Path, I would Rather Go Where There Is No Path And Leave A Trail."
"Ego is the worst thing many have, try to overcome it & you will be the best, if not good, person on this earth"