Anyplace cs-cart is installed on a single server with whatever would be considered a moderate load would slow it an any other software and website down.
Now if you created a server with cs-cart made an image in AWS, brought 3, 4 or more servers up with a load balancer, connected them to a master database and used (http://code.google.com/p/scalr/
) which auto scales your network monitors mysql and more, you have your self a highly scalable cs-cart system.
There's no defining though moderate load but cs-cart in the cloud would easily handle any load with the right network architecture. And anyone with a moderate load whatever that may be if their conversion rates were good should be thinking about scaling their site when needed. Average e-commerce startups are perfectly fine on shared hosts with private IP's for SSL etc.
Rackspace is also chearper than amazon, and maxCDN is much more affordable than akamai. There are plenty of ways to save money with both Amazon and Rackspace, as your only charged for live instances you can use their API's to put 100 servers online when needed and take them down and pay for what you use which is one big plus to cloud computing and paying for usage.