The stripe size how large your io has to be to get advantages from the raid.
With striped raids (0, and mirrored varaintions like like 10) you will get better read and writes when your io is larger than 64kb.
With parity raids (5,6, and mirrored varaintions like 50,60) you will get read advantages when your io is bigger than the stripe size, but no advantages for writing.
Without any caching this would be very noticable, but we have nowadays controllers with 1+ gb ram or features like cachecade/maxcache that can improve performance drastically. Especially with parity raids.