Pourquoi cette liste est-elle <>. Index de code si plus rapide que la liste [i] et manuelle comparer?

Je suis exécuté AQTime sur ce morceau de code, j'ai constaté que .indexof prend 16% du temps vs proche de 80% pour l'autre pièce ... Ils semblent utiliser les mêmes routines iséliques et autres. Appelé 116 000 fois l'insertion de 30 000 articles. Aucune de la liste Objets ne reçoit plus de 200 éléments. (J'utilise peut-être de manière incorrecte AQTime, je regarde cela)

class PointD : IEquatable<PointD>
{
    public double X, Y, Z;

    bool IEquatable<PointD>.Equals(PointD other)
    {
        return ((X == other.X) && (Y == other.Y) && (Z == other.Z));
    }
}

class PerfTest
{
    readonly List<PointD> _pCoord3Points = new List<PointD>();
    public int NewPoints;
    public int TotalPoints;

    public PerfTest()
    {
        NewPoints = 0;
        TotalPoints = 0;
    }
    public int CheckPointIndexOf(PointD pt)
    {
        int retIndex = _pCoord3Points.IndexOf(pt);
        if (retIndex < 0)
        {
            _pCoord3Points.Add(pt);
            NewPoints++;
        }
        TotalPoints++;
        return retIndex;    
    }

    public int CheckPointForBreak(PointD pt)
    {
        int retIndex = -1;
        for (int i = 0; i < _pCoord3Points.Count; i++)
        {
            PointD otherPt = _pCoord3Points[i];
            if ((pt.X == otherPt.X) &&
                (pt.Y == otherPt.Y) &&
                (pt.Z == otherPt.Z))
            {
                retIndex = i;
                break;
            }
        }
        if (retIndex == -1)
        {
            NewPoints++;
            _pCoord3Points.Add(pt);
        }
        TotalPoints++;
        return retIndex;
    }

    static void Main()
    {
        const int xmax = 300;
        const int ymax = 10;
        const int zmax = 10;
        const int imax = 4;

        var test = new PerfTest();
        //test.Init();
        Stopwatch sw = Stopwatch.StartNew();
        for (int i = 0; i < imax; i++)
        {
            for (int x = 0; x < xmax; x++)
            {
                for (int y = 0; y < ymax; y++)
                {
                    for (int z = 0; z < zmax; z++)
                    {
                        var pt = new PointD { X = x, Y = y, Z = z };
                        test.CheckPointIndexOf(pt);
                    }
                }
            }

        } 
        sw.Stop();
        string output = string.Format("Total: {0:0} New: {1:0} IndexOf: ", test.TotalPoints, test.NewPoints);
        Console.Write(output);
        Console.WriteLine(sw.Elapsed);

        test = new PerfTest();
        sw = Stopwatch.StartNew();
        for (int i = 0; i < imax; i++)
        {
            for (int x = 0; x < xmax; x++)
            {
                for (int y = 0; y < ymax; y++)
                {
                    for (int z = 0; z < zmax; z++)
                    {
                        var pt = new PointD { X = x, Y = y, Z = z };
                        test.CheckPointForBreak(pt);
                    }
                }
            }

        } 
        sw.Stop();
        output = string.Format("Total: {0:0} New: {1:0} PointD[] ", test.TotalPoints, test.NewPoints);
        Console.Write(output);
        Console.WriteLine(sw.Elapsed);
        Console.ReadLine();
    }
}