If you change 50 to (say) 1000 you are getting most of the benefits. The big problem you are trying to solve is "our password database just leaked; how fast ca

If you change 50 to (say) 1000 you are getting most of the benefits. The big problem you are trying to solve is "our password database just leaked; how fast can attackers figure out the passwords?" Say you can run SHA in 1 microsecond, and 1000 iterations in 1 millisecond. Even though it's 1000x slower, that's probably an unnoticeable difference as far as your performance is concerned. (YMMV) But, anyone trying to brute-force the passwords out of your database will now have to do 1000x the work. BTW, none of this will help you much if your users choose passwords like "abc" or "password". (IIRC scrypt lets you blow up in size as well as CPU, which makes GPUs impractical for attacking.)