Replace replace linq regex

gistfile1.cs

using System;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace ConsoleApplication1
{
	class Program
	{
		static void Main(string[] args)
		{
			Stopwatch stopWatch = new Stopwatch();
			String str = "123456#*42#";

			stopWatch.Start();
			for (int i = 0; i < 1000000; i++)
			{
				var result = str.Replace("*", "").Replace("#", "");
			}
			stopWatch.Stop();
			Console.WriteLine("Replace replace:" + stopWatch.ElapsedMilliseconds);

			stopWatch.Restart();
			for (int i = 0; i < 1000000; i++)
			{
				var tmp = new StringBuilder();
				var len = str.Length;
				for (int j = 0; j < len; j++)
				{
					if (str[j] != '#' && str[j] != '*')
						tmp.Append(str[j]);
				}
				var result = tmp.ToString();
			}
			stopWatch.Stop();
			Console.WriteLine("Stringbuilder replace:" + stopWatch.ElapsedMilliseconds);

			stopWatch.Restart();
			for (int i = 0; i < 1000000; i++)
			{
				var result = string.Join("",
				                         str.Select(r => char.IsDigit(r) ? r.ToString() : ""));
			}
			stopWatch.Stop();
			Console.WriteLine("Linq replace:" + stopWatch.ElapsedMilliseconds);

			stopWatch.Restart();
			for (int i = 0; i < 1000000; i++)
			{
				var result = Regex.Replace(str, @"[#\*]", string.Empty);
			}
			stopWatch.Stop();
			Console.WriteLine("Regex replace:" + stopWatch.ElapsedMilliseconds);
			Console.Read();
		}
	}
}

Example output:
Replace replace:220
Linq replace:694
Regex replace:1455

Added stringbuilder replace:
Replace replace:226
Stringbuilder replace:147
Linq replace:699
Regex replace:1459