KDF and number of iterations for GPG
Use gpg --s2k-mode 3 --s2k-count N, where N is the number of iterations you want to use.  The manual page says the default is 65536, and you can use any number between 1024 and 65011712.

If you like to tweak the defaults, I suggest making this number as large as you can bear it, without introducing noticeable slowdown (e.g., ideal would be to make the passphrase mangling process take about a second or so).

See also this answer to a different question, and the following questions/answers on IT Security.StackExchange:


What is purpose of --s2k-* GnuPG options?
gpg --perfect-code
an answer to "gpg encryption security"
an answer to "Good file encryption tools"
Do OpenPGP/GnuPG apply slow hash to password when encrypting/decrypting key?