Performance difference between to different expressions for the same thing

increment.cs

using System;
using System.Diagnostics;

namespace Bleh
{
    class Program
    {
        static void Main()
        {
            for (int i = 0; i < 5; i++)
            {
                var a = A();
                var b = B();
                Debugger.Log(0, "Performance", string.Format("The time difference is {0} ms.\r\n",  (Math.Abs(b - a) / (double)Stopwatch.Frequency) * 1000));
            }
        }

        public static unsafe long B()
        {
            var watch = Stopwatch.StartNew();

            int* data = stackalloc int[10000];
            int* ptr = data;
            for (int i = 0; i < 10000; i++)
            {
                *(ptr++) = 123;
            }

            watch.Stop();

            Debugger.Log(0, "Performance", string.Format("*(ptr++) = 123 took {0} ms.\r\n", (watch.ElapsedTicks / (double)Stopwatch.Frequency) * 1000 ));
            return watch.ElapsedTicks;
        }

        public static unsafe long A()
        {
            var watch = Stopwatch.StartNew();

            int* data = stackalloc int[10000];
            int* ptr = data;
            for (int i = 0; i < 10000; i++)
            {
                *ptr = 123;
                ptr++;
            }
            watch.Stop();

            Debugger.Log(0, "Performance", string.Format("*ptr = 123; ptr++ took {0} ms.\r\n", (watch.ElapsedTicks / (double)Stopwatch.Frequency) * 1000));
            return watch.ElapsedTicks;
        }
    }
}