This site has been working well on Surpass for a few months. Ski season over down here in Oz so not much traffic at the moment. MySQL on Surpass caches SQL queries from what I can gather (on Pass5 at least) and you can set up Xoops to cache as well (which is why I like it better than Mambo).....
http://www.eumarellah.com.au/
This Xoops has a hacked up menu system.... I'll do anything for a client!