I decided to give Google's Closure Compiler a try for this CMS. I'm really happy with the amount of compression you can obtain (I don't personally have exact numbers, but I know my largest Javascript asset compressed down by at least half). The one issue I have is the amount of time it takes (this link is a little old, but I can't find many new benchmarks comparing YUI and Closure: http://scoop.simplyexcited.co.uk/2009/11/24/yui-compressor-vs-google-closure-compiler-for-javascript-compression/).
This seems to speed page loading up a reasonable (at least noticeable) amount. I'd like to get the load time for adsense and analytics externals down, but overall it's not horrible. I'm going to set up Varnish for a reverse proxy cache and set up Redis for caching expensive database calls, once I've determined which are the most costly.