SurfWax LookAhead–Dynamic Search Navigation for RSS feeds is a search facility which suggests titles (in a alphabetical list) as you type the query…you can link to the native site from the suggestion box.
The other difference is you are only searching in the title element of the RSS feed and not in the body or actual content.
It would be good to separate blog content from traditional news content.
Updates hourly, and keeps the last 7 days worth of posts, and is sorted by date
…it doesn’t mention how many feeds they track.
See here for their marvellous site search service.