[lmz]

For SSL, aren't the individual packets encrypted with a symmetric cypher e.g. AES, RC4, 3DES, etc?

[caf]

Yes, the data stream is encrypted using a symmetric cipher, as the linked article says. The overhead of this is trivial.

It's the key exchange at the start of a session that requires the server to perform expensive RSA operations, which is why session caching helps.