Since Code Cloud plans to market itself as a Concrete5 Agency Partner, there wasn't any tool other than Concrete5 that we could use to create the site.
Working with the very latest C5 release, we had much more fun creating the site than we did working with 5.6.* release of Concrete5.
We're using nginx with Google's PageSpeed module compiled in and PHP CGI to run C5, a custom image caching server for serving responsive images and we plan to put Varnish in front of nginx soon to help boost performance further.
With a few configuration tweaks we've managed to get excellent ratings for both PageSpeed and YSlow (http://gtmetrix.com/reports/code-cloud.uk