Maximum number of RSS Feeds that can be run?

Hi

I installed the AutoBlog plugin and added one RSS Feed, Validated and Processed it.

9 Feed items were imported.
When I reopened my site I received a 500 Server Error - my web host increased the PHP Memory to 512mb and now I am able to login.

What is the total number of RSS Feeds I can run on my site at one time without it causing a major drain on server resources?
Thanks
Ken