WordPress Admin Overloading Server

Hi All,
I’ve a dedicated server and I host about 50 domains most of them are wordpress.

However for some reason the server is overloading and I’ve narrowed down to the WordPress Admin problem. Most often when server overloads I’m into admin and editing either post or configuring plugins.

I’ve done all optimization which might be possible viz. WP Super Cache, WP Minify, replacing the common php queries with static links, tracebacks and pingbacks disabled, post revision disabled, post revision table cleaned up from db, db optimized, etc. etc.

Following are typical plugins which I use:
All in SEO
Akismet
AVH Extended Categories Widgets
Configurable Tag Cloud
Dagon Design Sitemap Generato
Exclude Pages from Navigation
FeedBurner FeedSmith
GD Star Rating
Google XML Sitemaps
NoFollow Free
Robots Meta
Smooth Slider
Top Level Categories
Twitter Tools
Wordpress Thread Comment
WP-EMail
wp-insert
WP-PageNavi
WP Minify
WP Super Cache

Now I’m running out of ideas. Most of the above plugins are essential.

I used to have WordPress.com plugin as well but I remove it but it didn’t help either.

I’ve checked server logs but not getting anywhere as it doesn’t say anything about the wordpress plugins.

I’m running out of ideas.

Can anyone recommend how too find the problem and get it fixed.