Setting Safari SSL/TLS Cipher Suites
Unfortunately, AFAIK, this setting does not exist. (It doesn't exist in another WebKit browser, either: Google Chrome. You can do this in Firefox, though, using 'about:config'.)

About hard-coded cipher priorities/support for the SSL/TLS handshake:

I tested that Safari does not support 40-bit RC4 encryption with an MD5 hash. This means that it does not support some products that are required by US export law to use low (&lt;64-bit) encryption.

See also:

http://www.carbonwind.net/blog/post/A-quick-look-over-some-browsers-and-their-SSLTLS-implementations.aspx

"Initially, in SSL/TLS negotiations, TLS with RSA and weak 128-bit RC4 keys are offered first and second in the cipher order. Worse, ECC (Elliptical Curve Cryptography), AES (Advanced Encryption Standard), and 256-bit keys are never offered as potential cipher choices; further, MD5 is offered first and more frequently than SHA-1, when it should be the other way around."

By Roger A. Grimes, Infoworld    Feb 1, 2009 1:19 pm 

http://www.pcworld.com/article/158706/how_secure_is_safari.html