Configuring predictable IPv6 addresses for laptop client
Just a small correction, but OSX (at least Mountain Lion) has full DHCPv6 client, which works out of the box to communicate with a DHCPv6 server on your network.  The case may be, that Apple Airport does not have a DHCPv6 server and therefore your choice of IPv6 assignment is limited to auto-configuration (SLAAC) and link-local schemes (the ones controlled by privacy setting).

The SLAAC address, as you correctly worked out, uses the last three octets of the L2 MAC address.  The other address is the link-local address of the interface.

If you wanted to use a DHCPv6 assignment, then you would run a small inexpensive DHCPv6 server on your network and end up with a third IPv6 address from your chosen DHCP scope, configured on your interfaces (depending on privacy setting).

If you combine this DHCPv6 server with your own DNS server, and configure delegation, you could just use DNS names rather than relying on IPs.

Reference:

http://blog.ipspace.net/2012/11/ipv6-router-advertisements-deep-dive.html
http://blog.belodedenko.me/2013/06/a-practical-guide-to-setting-up-ipv6.html
http://en.wikipedia.org/wiki/Link-local_address#IPv6