Post & Comment Archiving?

Hi. I administer footballoutsiders.com, an NFL Football site that gets 10000 visits/day. We’re having issues with queries overloading the server, and I was wondering about the ability to archive posts & comments…mostly the comments. In the three years of the site’s existence, we’ve had 2700 posts and about 140,000 comments, and apparently WP searches all 140,000 every time it does any query involving comments.

It would be great to be able to take the older posts and essentially make them static, so that mySQL doesn’t have to search everything. Does such a thing exist?

The site uses the following plugins:
Adhesive 2.1 (sticky posts)
Comment Plugger 1.01 (gives last person to comment on each post)
Customizable Post Listings 1.1 (5 most recent posts, most recently commented posts)
Page Navigation 1.5
wp-cache2

Thanks…