I'd start slow.  Just disable the Ajax setting.  Some folks have found that to help.  I would not touch the cache setting.  The other thing to understand is using more feeds in the module instance is going to take longer to download and transform. 

I'm not a fan of the aggregation feature of the module, so I don't use it in that manner.  I use the Feed Explorer for aggregating feeds, and the older version of the News module v3.0.1.  If you look at the posts at the top of this forums, you'll see many reports of failed feeds.  Inspection of other posts, shows the many issues folks are running into with the v4.0.x module. 

As an alternative, I even use the XML/XSL module with custom XSL files to render news feeds.

Another important point is before using any module, I always test in a non-production site. 

I don't know the exact answer to your particular issue, as there are many 'gotchas' along the way, including site configuration.  However, I'd start slow, using 1 feed in the module to see if that works, then progress slowly adding another.  I don't know at what point you would see significant slowness in rendering, but sounds like 6 feeds is beyond the practical limit.  How many items are in each?  Even if you limit the number of entries to show, you will only impact the first feed, not x number from every feed.

Yes, I would agree that the 2 day time-out is strange behaviour, but then again, there are many possibilities for it, not just the news module itself.  The cache settings only manages the amount of time the data should be resident for quicker access, either from memory, or disk.  The process is supposed to improve response times by having the feed content available for use, rather than making another round of web requests to retrieve the feed.  Again, that's the way it is supposed to work, but there are reports of the caching, and scheduling tasks not working properly, which I cannot really speak about with any authority.

I do not modify the cache settings myself, I leave it alone.

The Feed Explorer is available from the modules dropdown box.  Either using the Admin, or Host account you can add a module to a page, the modules available for use are displayed in that modules dropdown box.  You should see the Feed Explorer listed there.  It is a bit difficult to set up, as it does require some knowledge of OPML.  However, once you get a handle on it, in my opinion, offers a better way to aggregate newsfeeds.  You will need to know OPML to effectively use it, though.  I've got some posts with example OPML files, and have blogged about it on my blog. (blog1, blog2) Might be worth your time to read the blogs and search for OPML examples, I've posted, including the first post I made in the forums about it - here.  One thing about this module is it comes with no seperate forum or documentation, so read my first post about it, because it has a lot of information, and a note about how to use it from the creator, Nik, himself.