c# - \d less efficient than [0-9] - Stack Overflow

I made a comment yesterday on an answer where someone had used [0123456789] in a regex rather than [0-9] or \d. I said it was probably more efficient to use a range or digit specifier than a character set.

I decided to test that out today and found out to my surprise that (in the c# regex engine at least) \d appears to be less efficient than either of the other two which don't seem to differ much. Here is my test output over 10000 random strings of 1000 random characters with 5077 actually containing a digit:

Regex \d took 00:00:00.2141226 result: 5077/10000
Regex [0-9] took 00:00:00.1357972 result: 5077/10000 63.42 % of first
Regex [0123456789] took 00:00:00.1388997 result: 5077/10000 64.87 % of first

It's a surprise to me for two reasons, that I would be interested if anyone can shed some light on:

Here is the test code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Diagnostics;
using System.Text.RegularExpressions;
namespace SO_RegexPerformance
{
 class Program
 {
 static void Main(string[] args)
 {
 var rand = new Random(1234);
 var strings = new List<string>();
 //10K random strings
 for (var i = 0; i < 10000; i++)
 {
 //generate random string
 var sb = new StringBuilder();
 for (var c = 0; c < 1000; c++)
 {
 //add a-z randomly
 sb.Append((char)('a' + rand.Next(26)));
 }
 //in roughly 50% of them, put a digit
 if (rand.Next(2) == 0)
 {
 //replace 1 char with a digit 0-9
 sb[rand.Next(sb.Length)] = (char)('0' + rand.Next(10));
 }
 strings.Add(sb.ToString());
 }
 var baseTime = testPerfomance(strings, @"\d");
 Console.WriteLine();
 var testTime = testPerfomance(strings, "[0-9]");
 Console.WriteLine(" {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
 testTime = testPerfomance(strings, "[0123456789]");
 Console.WriteLine(" {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
 }
 private static TimeSpan testPerfomance(List<string> strings, string regex)
 {
 var sw = new Stopwatch();
 int successes = 0;
 var rex = new Regex(regex);
 sw.Start();
 foreach (var str in strings)
 {
 if (rex.Match(str).Success)
 {
 successes++;
 }
 }
 sw.Stop();
 Console.Write("Regex {0,-12} took {1} result: {2}/{3}", regex, sw.Elapsed, successes, strings.Count);
 return sw.Elapsed;
 }
 }
}