SilverStripe is fastest when served from a cache. memcached or using some other form of opcode cache helps dramatically. I think one of the issues with running on the GS is that it cannot work off a single cache as easily so more processing time is taken up rebuilding the cache as its all around.
If you setup a 'silverstripe-cache' folder in your root site directory then that will be a benefit.
I run about eight to ten SilverStripe websites on both Media Temple GS and DV servers. My experience is, if you upgrade to the DV server, that alone will give SS a giant boost in speed. On the GS, it is noticeably slower. But like Willr said, enabling caching will help. You could also look into the module that converts your pages to static HTML, for even better performance boosts.
I am running a Silverstripe install on Media Temple dv 3.5.
I am having a problem getting my cache blocks to work. I have my 'silverstripe-cache' directory permissions at 777, but nothing is being written to the 'cache ' folder within the 'silverstripe-cache' folder (no zend files). Therefore my partial cacheing is not working. My cache folder has permissions of 'owner: apache' and 755.
Have you ever experienced anything like this on Media Temple?
i create a cache-folder inside the data folder from my media template account. so that it is siblings to the tmp folder where the php sessions are stored. i'm not 100% sure, if it's the best way, but it works...
Setting the permissions to 777 and changing the owner and group of the silverstripe-cache/cache folder did the trick. Media Temple automatically assigned an owner and group of apache to the cache folder.
Getting APC installed on dv 3.5 was a whole other bag of worms. I finally did get it installed, but whenever I up the shared memory to 128M, CPU usage peaks out on me. Right now I have shared memory set to 100M and everything seems to be holding steady.