Standard optimization. My.cnf modifications, tweaks to httpd.conf, etc. Other than that all you can really do is swap out software (e.g replace Apache with Lighttpd or similar, etc).
You cant tell me your 'special optimized XenForo VPS' has some kind of unique feature that isn't found in every single other VPS, can you? (BTW, just want to point out - I'm not trying to be an ass or anything - just having a bit of fun as I can see a bunch of hosts coming out with a bunch of marketing crap about how they are the best XenForo host to make a quick sale, and was intrigued as to how yours is better/different
)