HashSet<char>.Contains(c) versus string.Contains(c)

hashset.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Linq;

struct Program
{
	static void Main()
	{
		const int iterations = 10000000;

		string smallString = "<>*";
		string largeString = "@<>d+-0123456789abcdefghijklm<#";
		string testChars = "sglkjhw!%6*&^)()vxz.,mnbc/.qeRHD4rloi2405,nas@%%^*$%*dsfskh32XCBW5643g";

		var smallSet = new HashSet<char>(smallString);
		var largeSet = new HashSet<char>(largeString);

		Benchmark("String, small", iterations, x => smallString.Contains(testChars[x % testChars.Length]));
		Benchmark("String, large", iterations, x => largeString.Contains(testChars[x % testChars.Length]));
		Benchmark("HashSet<char>, small", iterations, x => smallSet.Contains(testChars[x % testChars.Length]));
		Benchmark("HashSet<char>, large", iterations, x => largeSet.Contains(testChars[x % testChars.Length]));
	}

	static void Benchmark(string title, int iterations, Action<int> code)
	{
		var sw = Stopwatch.StartNew();
		for (var i = 0; i < iterations; i++)
		{
			code(i);
		}
		sw.Stop();
		Console.WriteLine("{2} Time elapsed: {0}, single iteration: {1} ms", sw.Elapsed, sw.Elapsed.TotalMilliseconds / iterations, title);
	}
}