sevenspark

The new accessibility javascript in the Appearance > Menus panel in WordPress 3.6 can significantly slow the page load speed when using a large number of menu items (> 50). This plugin defers the accessibility processing to eliminate the scripting bottleneck and allow the Appearance > Menus screen to run much faster and more responsively.
<a href="http://sevenspark.com/wordpress/speeding-up-the-appearance-menus-screen-in-wordpress-3-6" rel="nofollow ugc">Full details</a>
This solution is fairly rough. Hopefully we can develop a robust solution that can eventually become part of the core. Pull requests through GitHub are welcome.

Faster Appearance – Menus

Mr Pete

The (mu-compatible) WP Tuner plugin for WordPress is a powerful and easy to use way to answer many hard questions about why your blog is slow or cranky. What’s causing the slowdown? Is it a plugin? Is it your host?
Used with a bit of common sense, this powerful plugin will help blog administrators as well as software developers improve their WordPress blog performance.
Perfect for WordPress site administrators, plugin and theme designers, developers
Fully translatable.
<h3>Advanced Use</h3>
Here are more advanced ways to make use of WP Tuner. Please <a href="http://blogs.icta.net/plugins/wptuner" title="(Visit the WP Tuner home page)" rel="nofollow ugc">share your questions and/or stories</a> examples to share with others!
1) Hook any WordPress action
In wptuner.php, you will find a default set of action hooks. You can add as many hooks as you like for other actions. They look like this (just change “admin_footer” to the name of the action you want to measure):
<pre><code>add_action('admin_footer', 'wpTuneFilterTime' );
</code></pre>
Each hook adds a line to the WP Tuner performance analysis table, when that action is triggered.
2) Time anything at all in WordPress
WP Tuner contains a function that causes performance analysis for any section of WordPress code. Just use 
 wpTuneMarkTime(‘My Marker string’);
…at the beginning of the code you want analyzed. Add another marker at the end if needed.
For example, suppose you want to know how much time is spent loading each of the plugins you have enabled. Here’s how to do it, by adding two simple lines to wp-settings.php:
<pre><code>if (function_exists(wpTuneMarkTime)) wpTuneMarkTime('Load Plugins'); // ** Add THIS line **

if ( get_option('active_plugins') ) {
 $current_plugins = get_option('active_plugins');
 if ( is_array($current_plugins) ) {
 foreach ($current_plugins as $plugin) {
 if (function_exists(wpTuneMarkTime)) wpTuneMarkTime('Plugin: '.$plugin); // ** Add THIS line **
 if ( '' != $plugin && 0 == validate_file($plugin) && file_exists(WP_PLUGIN_DIR . '/' . $plugin) )
 include_once(WP_PLUGIN_DIR . '/' . $plugin);
 }
 }
}<h3>Credits</h3>
</code></pre>
Many thanks to the WP Tuner translation team!
Русский: <a href="http://lecactus.ru" rel="nofollow ugc">Кактусу</a> (updated through WP Tuner 0.9.3)
<h3>Readme Validator</h3>
This readme was validated using: 
<a href="https://wordpress.org/extend/plugins/about/validator/" rel="ugc">https://wordpress.org/extend/plugins/about/validator/</a>

WP Tuner

Easily, powerfully, discover why your blog or plugin is slow or cranky. Comprehensive time and database access analyzer. WPmu. multi-lingual.

Faster Appearance – Menus vs WP Tuner