LINQ と foreach どっちが速い！？ (Except)

LinqVsForEach

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace LinqVsForEach
{
    class Program
    {
        static void Main(string[] args)
        {
            // 要素数を変えて試してみる
            var lengths = new int[] {10, 100, 1000, 10000, 100000, 1000000, 10000000, 50000000};

#if NETCOREAPP1_1
            Console.WriteLine(".NET Core 1.1");
#elif NET461
            Console.WriteLine(".NET Framework 4.6.1");
#endif

            Console.WriteLine("Length\toreore\tganbatta\tlinq");

            foreach (var length in lengths)
            {
                (long oreore, long ganbatta, long linq) = Test(length);
                Console.WriteLine($"{length}\t{oreore}\t{ganbatta}\t{linq}");
            }
        }

        private static (long oreoreMilliSec, long ganbattaMilliSec, long linqMilliSec) Test(int length)
        {
            // 10 回やる
            const int loop = 10;

            var first = Enumerable.Range(1, length * 2);
            var second = Enumerable.Range(1, length);

            // オレオレ手抜き Except
            // 遅すぎて無理。。。
            //var oreoreSw = new Stopwatch();
            //oreoreSw.Start();
            //Repeat(() => first.OreOreExcept(second).ToArray(), loop);
            //oreoreSw.Stop();

            // オレオレがんばった Except
            var ganbattaSw = new Stopwatch();
            ganbattaSw.Start();
            Repeat(() => first.OreOreGanbattaExcept(second).ToArray(), loop);
            ganbattaSw.Stop();

            // LINQ の Except
            var linqSw = new Stopwatch();
            linqSw.Start();
            Repeat(() => first.Except(second).ToArray(), loop);
            linqSw.Stop();

            return (0, ganbattaSw.ElapsedMilliseconds, linqSw.ElapsedMilliseconds);
        }

        private static void Repeat(Action action, int count)
        {
            for (var i = 0; i < count; i++)
            {
                action();
            }
        }
    }

    internal static class OreOreExtensions
    {
        public static IEnumerable<T> OreOreExcept<T>(this IEnumerable<T> first, IEnumerable<T> second)
        {
            foreach (var elem in first)
            {
                foreach (var secondElem in second)
                {
                    if (elem.Equals(secondElem))
                    {
                        yield return elem;
                        break;
                    }
                }
            }
        }

        public static IEnumerable<T> OreOreGanbattaExcept<T>(this IEnumerable<T> first, IEnumerable<T> second)
        {
            var set = new HashSet<T>(second);

            foreach (var elem in first)
            {
                if (set.Add(elem))
                {
                    yield return elem;
                }
            }
        }
    }
}