Stress from bolded lines of unread articles can be overwhelming.
In FeedDemon, a desktop based reader, there is a tool called the Panic button that is triggered when you have a lot of unreads (or that you can trigger manually). It displays the following message:
You have 591 unread articles. This isn't email - you don't have to read everything. Perhaps it's time to hit the panic button and let FeedDemon mark articles as read for you?
Then you can mark all articles older than say 48H or 5 days as read automatically.
As a basic feature you can group feeds and there is a button that let you mark all articles in a group (or a single feed) as read, so for chatty feeds you can just skim the titles and if nothing mandates further reading you can clear it up.
The real trick though for me is to revisit your RSS list regularly, say once a year, and not be afraid to remove or filter feeds that post too many articles. Some big blogs in their niche post several "news" pieces per day.
What was great was Yahoo Pipes, where you could filter, merge and transform feeds into new feeds. So you could grab a feed from a chatty blog and filter it on some keyword for the subniche you are interested in, then do that on several sources and merge all these into one consolidated feed.