For all x-cart's strengths, speed is certainly not one of them. There are however steps you can, and should, take to speed up your x-cart. Here is the most complete listing of x-cart speed optimization tips available. Thanks to NuAlpha, B00MER, Connor and Emerson for their contributions:

Administration Changes

The following changes can be made in your X-Cart admin section:

• Ensure your images are in the file system, not in your database.
• Disable extra functions and modules that you do not need.
• The Advanced Statistics module slows down x-cart by storing statistical information in the database. We highly recommend you disable the advanced statistics module and use a log file analyzer and/or a program such as Marketing Manager.

Files/Setup

• Move javascript to .js includes and css to .css includes so that they can be better cached.
• Optimize your html code so that it is clean and efficient, limit your use of tables, and optimize the size of your images and product thumbnails.
• X-Cart provides an addon called "Fancy Categories" - don't use it.
• If you use a linux server, edit/create your .htaccess file to include the following:
  
  php_flag zlib.output_compression On
  php_value zlib.output_compression_level 2
  
• Smarty provides a method to increase speed by caching the templates so they do not need to be recompiled. This should NOT be used when you are making changes to your site templates, as no template changes will be recognized while the check is disabled. So if making changes, you will need to ensure this variable is set to "true."
  
  You can enable template caching by opening the file "Smarty.class.php" in your smarty directory and editing this variable to "false":
  
  /**
  * This tells Smarty whether to check for recompiling or not. Recompiling
  * does not need to happen unless a template or config file is changed.
  * Typically you enable this during development, and disable for
  * production.
  *
  * @var boolean
  */
  var $compile_check = true;

Database

• It is very important to optimize all of your x-cart tables in your database on a regular basis. There is a script posted on the x-cart forums which will allow you to do this:
  http://forum.x-cart.com/viewtopic.php?t=11585

Server Level

If you are on a dedicated server you will have access to do the following, if not, you may need to speak to your web host.

• Install Zend Optimizer and Ioncube.
• Ensure your server has lots of RAM.
• Have your MySQL settings optimized for your particular needs.
• Use linux's "top" function to monitor your server load. If your server load is above 1.00 and it cannot be lowered with optimization, it is too high and you may want to look at a hosting/server upgrade.

Additionally

• When programming your site, or hiring someone else to program for you, make sure you/they know what you/they are doing! It is very dangerous for a coder to know enough to modify code but not enough to modify it correctly.