Benchmark for IsStringMadeOf

//Tested with 7289505 random inputs.

    // 44 seconds
    public static bool IsStringMadeOf1(this string str, string from)
        {
            if (str.Length > from.Length) return false;

            for (int i = 0; i < str.Length; i++)
            {
                int index = from.IndexOf(str[i]);
                if (index != -1)
                {
                    from = from.Remove(index, 1);
                }
                else
                {
                    return false;
                }
            }
            return true;
        }

    // 59 seconds
    public static bool IsStringMadeOf2(this string str, string from)
        {
            if (str.Length > from.Length) return false;

            Dictionary<char, int> seqSource = str.GroupBy(c => c)
                .ToDictionary(key => key.Key, value => value.Count());

            Dictionary<char, int> seqTest = from.GroupBy(c => c)
                .ToDictionary(key => key.Key, value => value.Count());

            int count;

            foreach (var kvp in seqSource)
            {
                if (!seqTest.TryGetValue(kvp.Key, out count) || kvp.Value > count) return false;
            }

            return true;
        }

    // 45 seconds
    public unsafe static bool IsStringMadeOf3(this string str, string from)
        {
            if (str.Length > from.Length) return false;

            var copy = new char[from.Length];
            from.CopyTo(0, copy, 0, copy.Length);
            fixed (char* s = str)
            {
                fixed (char* f = copy)
                {
                    var l = str.Length;
                    for (int i = 0; i < l; ++i)
                    {
                        var index = Array.IndexOf(copy, s[i]);
                        if (index != -1)
                            f[index] = '\0';
                        else
                            return false;
                    }
                    return true;
                }
            }
        }

    // 105 seconds
        public static bool IsStringMadeOf4(this string str, string from)
        {
            if (from.Except(str).Count() == from.Length - str.Length)
                return true;
            return false;
        }