My limited tests show that Dictionary is faster than `SortedList`. The latter uses `Array.BinarySearch` to find entries. I have read other performance tests that report binary searches to be faster for small numbers of keys. I checked this on my MacBook Pro - and the Dictionary approach was twice as fast with 10 keys and hundreds of times faster will 1000 or more keys. That is not to say that the results would be the same on other hardware - an Android phone for example.