Test Code

 
                Test("Regular Loop", () =>
                {
                    var itemx = GetList(list, list2);
                });

                Test("Regular Loop2", () =>
                {
                    var itemx = GetList2(list, list2);
                });


                Test("Linq", () =>
                {
                    var itemx = (
                        from x in list
                        join y in list2 on x.ID equals y.ID
                        select new DataHolder { x = x, y = y }
                        ).ToList();
                    //var ik = "";
                });

Test Method

static void Test(string name, Action action)
        {
            var sw = new Stopwatch();
            sw.Start();
            for (var i = 0; i < MAX_COUNT; i++)
            {
                action();
            }
            sw.Stop();
            Console.WriteLine("Completed {0} in {1} Millisecond(s)", name, sw.ElapsedMilliseconds);
        }

https://gist.github.com/anonymous/6942121