Benchmark C# collections

Benchmark.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            var nums1 = Enumerable.Range(1, 1000).ToList();
            var nums2 = Enumerable.Range(2000, 5000).ToList();
            nums2.Add(50);

            var iterations = 10000;

            Benchmark(nums1, nums2, iterations, Intersect1, "Double iteration");
            Benchmark(nums1, nums2, iterations, Intersect3, "HashSet");
            Benchmark(nums1, nums2, iterations, Intersect2, "Dictionary");

            Console.WriteLine("Press any key ...");
            Console.ReadKey(true);
        }

        private static void Benchmark(List<int> nums1, List<int> nums2, int iterations, Func<List<int>, List<int>, int?> action, string name)
        {
            Console.WriteLine("Executing: {0}", name);
            var watch = Stopwatch.StartNew();
            var v = action(nums1, nums2);
            for (var i = 0; i < iterations; i++)
            {
                action(nums1, nums2);
            }
            watch.Stop();

            Console.WriteLine("result: {0}", v);
            Console.WriteLine("elapsed time: {0}", watch.ElapsedMilliseconds);
        }

        static int? Intersect3(List<int> nums1, List<int> nums2)
        {
            var hashSet = new HashSet<int>(nums1);
            foreach (var i in nums2)
            {
                if (hashSet.Contains(i))
                    return i;
            }

            return null;
        }

        static int? Intersect2(List<int> nums1, List<int> nums2)
        {
            var dictionary = nums1.ToDictionary(i => i);

            foreach (var i in nums2)
            {
                if (dictionary.ContainsKey(i))
                    return i;
            }

            return null;
        }

        static int? Intersect1(List<int> nums1, List<int> nums2)
        {
            for (int i = 0; i < nums1.Count; i++)
            {
                var n = nums1[i];
                for (int j = 0; j < nums2.Count; j++)
                {
                    var m = nums2[j];
                    if (n == m)
                        return n;
                }
            }

            return null;
        }
    }
}