static class Program
    {
        struct ValueHolder
        {
            private readonly long _value;

            public ValueHolder(long value)
            {
                _value = value;
            }
        }
        struct ValueHolderNullable
        {
            private readonly long? _value;

            public ValueHolderNullable(long? value)
            {
                _value = value;
            }
        }
        
        static void Main(string[] args)
        {
            Console.WindowWidth = 120;

            var data = Enumerable.Range(0, 10000)
                .Select(i => (long)i % 1000)
                .ToArray();

            var data2 = data.Select(l => new ValueHolder(l)).ToArray();

            var data3 = data.Select(l => new ValueHolderNullable(l)).ToArray();

            // Замеры начались
            Measure("Raw", () =>
            {
                data.Distinct().ToArray();
                return data.Length;
            });

            Measure("Wrapper", () =>
            {
                data2.Distinct().ToArray();
                return data2.Length;
            });

            Measure("NullableWrapper", () =>
            {
                data3.Distinct().ToArray();
                return data3.Length;
            });
            // Замеры закончились

            Console.WriteLine("Done.");
            Console.ReadKey();
        }

        static void Measure(string name, Func<long> callback)
        {
            GC.Collect();
            GC.WaitForPendingFinalizers();
            GC.Collect();

            var mem = GC.GetTotalMemory(true);
            var gc00 = GC.CollectionCount(0);
            var gc01 = GC.CollectionCount(1);
            var gc02 = GC.CollectionCount(2);

            var sw = Stopwatch.StartNew();
            var result = callback();
            sw.Stop();

            var mem2 = GC.GetTotalMemory(false);
            var gc10 = GC.CollectionCount(0);
            var gc11 = GC.CollectionCount(1);
            var gc12 = GC.CollectionCount(2);

            var memDelta = (mem2 - mem) / 1024.0;
            var gcDelta0 = gc10 - gc00;
            var gcDelta1 = gc11 - gc01;
            var gcDelta2 = gc12 - gc02;

            Console.WriteLine(
                "{0,20}: {1,5}ms, ips: {2,22:N} | Mem: {3,9:N2} kb, GC 0/1/2: {4}/{5}/{6} => {7,6}",
                name, sw.ElapsedMilliseconds, result / sw.Elapsed.TotalSeconds, memDelta, gcDelta0, gcDelta1, gcDelta2, result);
        }
    }

                 Raw:     2ms, ips:           3 674 849,33 | Mem:     84,02 kb, GC 0/1/2: 0/0/0 =>  10000
             Wrapper:     5ms, ips:           1 958 288,46 | Mem:    519,83 kb, GC 0/1/2: 0/0/0 =>  10000
     NullableWrapper:  2759ms, ips:               3 623,46 | Mem:    655,90 kb, GC 0/1/2: 229/0/0 =>  10000
Done.