In response to #1: The idea of javascript being "unobtrusive" is related to semantics more than efficiency. Putting an onclick inside of an <a> clutters the code with script. Keeping your event handlers in an external file is good for the same reasons that you keep your css in an external file instead of inline.
There's a great article over at A List Apart that mentions the onclick issue: http://www.alistapart.com/articles/behavioralseparation
