Linking to specific entries in Twig: How performant is Reference Tags parsing?
If you turn on debug mode in your config file, and then create an ultra simple template with just these code options in it, you should be able to look at the logs in the console. It should tell you the query time in milliseconds. I've never used reference tags; however, I  would suspect that the performance difference is minimal. I personally would opt for the second method, so that entry.title is not hard coded.

As a side note, you can also wrap the code in {% cache %}... {% endcache %} tags to further increase performance either way.