IndexOf いろいろ比較。

Program.cs

using System;

namespace StringIndexOfSpeedTest
{
	class Program
	{
		static void Main( string[] args )
		{
			var data = "bbbbbbbbbbbbbbbbbbbbbbbbbbb[bbbbbbbbbbbbbbbbbbbbbbbbbbb";
			var find = '[';
			var count = 10000000;
			var io1 = GetTime( DefaultIndexOf, count, data, find );
			var io2 = GetTime( IndexOfIndexer, count, data, find );
			var io3 = GetTime( IndexOfPointer, count, data, find );

			Console.WriteLine( "DefaultIndexOf:\t{0}", io1 );
			Console.WriteLine( "IndexOfIndexer:\t{0}", io2 );
			Console.WriteLine( "IndexOfPointer:\t{0}", io3 );
			Console.ReadKey( true );
		}

		static TimeSpan GetTime( Func<string, char, int> ex, int count, string data, char find )
		{
			var start = DateTime.Now;

			var c = 0;
			while( c++ < count )
			{
				ex( data, find );
			}

			var end = DateTime.Now;

			return end - start;
		}

		static int DefaultIndexOf( string data, char find )
		{
			return data.IndexOf( find );
		}

		static int IndexOfIndexer( string data, char find )
		{
			var dataLength = data.Length;

			int pos = 0;
			while( pos < dataLength )
			{
				if( data[pos] == find )
				{
					break;
				}
				++pos;
			}
			if( pos == dataLength )
			{
				pos = -1;
			}
			return pos;
		}

		unsafe static int IndexOfPointer( string data, char find )
		{
			fixed( char* begin = data )
			{
				char* ptr = begin;
				char* end = begin + data.Length;
				while( ptr < end )
				{
					if( *ptr == find )
					{
						break;
					}
					++ptr;
				}
				if( ptr == end )
				{
					return -1;
				}
				return ( int )( ptr - begin );
			}
		}
	}
}

Result.txt

.NET Framework 4.5.2, Release build
Core i7-4500U で実行

--- Result ---
DefaultIndexOf: 00:00:00.3310381
IndexOfIndexer: 00:00:01.5193548
IndexOfPointer: 00:00:00.7990235