+Circloscope Premium is an excellent tool for circle management:
The new paid version costs 47 USD.
It is very versatile!
+martin shervington wrote an excellent post about the uses of Circloscope Premium:
I recommend using Circloscope to manage you circles, not only when you get close to the 5000 limit.
Here is the extension: http://goo.gl/RQVFp it costs $47 for premium and is well worth it.
I was doing so circle adjustment yesterday and thought just how great a tool this is!
Here is a list of easy to follow 'recipes' you will find in the app. Very straightforward, and is on hand to help you out too. Hope it helps to get your circles in order.