Interface based iterations improve the performance?

Yes, All Collections implements the one more collection is called IEnumerable. this IEnumerable has one       method is called   GetEnumerator()

again this GetEnumerator() return type is IEnumerator,IEnumerator has few methods which are helpful to

iterate through all the element in that collection.

Ex: In our framework many collections(ArrayList,SortedList,Hasttable..ect)..implements the

class  ArrayList : IList, ICollection, IEnumerable, ICloneable

{

   public virtual IEnumerator  GetEnumerator(); //  used to  get the elements of the apporiate type

}

What is IEnumerable ?

IEnumerable is an interface which is to used  define with few members which are used to iteration of same type of their apporiatecollections.

not only ArrayList.all collections(sortedlist,hasttable,...ect) we can iterate like this. way because all collections implements
this IEnumerator Interface.
   as well as we can iterate through Array types also. way because these array class implements the IEnumerable interface.

the Array can be string,int, bool..any array we can iterator through IEnumerable manner.

Example:

      

so we can iterate through any type array it can be int,string,bool,float..ect