Large Drupal sites are renowned for being fairly resource heavy when it comes to MySQL queries and that sort of thing. The in-built Drupal performance settings and some modules like Boost do help, but you really need to make environmental changes to get the best performance.
Significant cache and pre-compilation improvements can be made using code, database and proxy accelerators like APC, Zend Optimizer and Memcached. The problem with these is that they can be difficult, if not impossible, to install on shared hosting. Below are some online resources I've found which related to getting some of these installed on 1&1's shared hosting via SSH access.
Memcached MySQL query caching
Zend Optimizer PHP precompilation
PECL UploadProgress - not for performance but something I came across
Using SSH on 1&1 shared hosting