How can I crawl/index only 5 site collections without losing the crawled/indexed other site collections?

I am using SP 2010 and FAST Search. I have a contentsource for the webapplication url "intranet.myCompany.com". This is working, but very slow. I would like to create some content source for only 5 site collections:

http://ift.tt/1Ds7T6y
http://ift.tt/1I0heCg
http://ift.tt/1Ds7ReU
http://ift.tt/1I0heCn
http://ift.tt/1Ds7ReY

Is this possible or do I need to remove the existing content source? I do not want to lose all the current crawled/indexed site collections (crawled already by the current content source)