I have a map view with a large quantity of annotations (3000+), when the user is zoomed to a reasonable level all is well and fast.
Although when the user zooms out and
I ended up grouping my annotations in clusters using OCMapView. Its free, and very easy to implement into existing code.
It automatically groups your annotations when zoomed out and as you zoom in they appear unclustered as they should.
I know this is an old question but its a great option for anyone else trying to do the same thing.