加快搜索速度.net 4.0

想知道是否可以加快搜索速度。我需要构建一个必须被许多UI屏幕使用的功能我有一个工作，但我需要确保我正在实现一个快速算法，如果你喜欢

这就像一个增量搜索。

用户键入要搜索的单词，例如

        const string searchFor = "Guinea";
        const char nextLetter = ' '

它在列表中查找并返回2条记录

     "Guinea and Guinea Bissau "

用户键入要搜索的单词，例如

        const string searchFor = "Gu";
        const char nextLetter = 'i'
    returns
    3 results.

这是函数，但我想加快它的速度。这种搜索有模式吗？

class Program
{
    static void Main()
    {
        //Find all countries that begin with string + a possible letter added to it
        //const string searchFor = "Guinea";
        //const char nextLetter = ' ';  //returns 2 results
        const string searchFor = "Gu";
        const char nextLetter = 'i';
        List<string> result = FindPossibleMatches(searchFor, nextLetter);
        result.ForEach(x=>Console.WriteLine(x)); //returns 3 results

        Console.Read();
    }
    /// <summary>
    /// Find all possible matches 
    /// </summary>
    /// <param name="searchFor">string to search for</param>
    /// <param name="nextLetter">pretend user as just typed  a letter</param>
    /// <returns></returns>
    public static List<string> FindPossibleMatches (string searchFor, char nextLetter)
    {
        var hashedCountryList = new HashSet<string>(CountriesList());
        var result=new List<string>();
        IEnumerable<string> tempCountryList = hashedCountryList.Where(x => x.StartsWith(searchFor));
        foreach (string item in tempCountryList)
        {
            string tempSearchItem;
            if (nextLetter == ' ')
            {
                tempSearchItem = searchFor;
            }
            else
            {
                tempSearchItem = searchFor + nextLetter;
            }
            if(item.StartsWith(tempSearchItem))
            {
                result.Add(item);
            }
        }
        return result;
    }

    /// <summary>
    /// Returns list of countries.
    /// </summary>
    public static string[] CountriesList()
    {
        return new[]
            {
                "Afghanistan", "Albania", "Algeria", "American Samoa", "Andorra",
                "Angola", "Anguilla", "Antarctica", "Antigua And Barbuda", "Argentina",
                "Armenia", "Aruba", "Australia", "Austria", "Azerbaijan",
                "Bahamas", "Bahrain", "Bangladesh", "Barbados", "Belarus",
                "Belgium", "Belize", "Benin", "Bermuda", "Bhutan",
                "Bolivia", "Bosnia Hercegovina", "Botswana", "Bouvet Island", "Brazil",
                "Brunei Darussalam", "Bulgaria", "Burkina Faso", "Burundi", "Byelorussian  SSR",
                "Cambodia", "Cameroon", "Canada", "Cape Verde", "Cayman Islands",
                "Central African Republic", "Chad", "Chile", "China", "Christmas Island",
                "Cocos (Keeling) Islands", "Colombia", "Comoros", "Congo", "Cook Islands",
                "Costa Rica", "Cote D'Ivoire", "Croatia", "Cuba", "Cyprus",
                "Czech Republic", "Czechoslovakia", "Denmark", "Djibouti", "Dominica",
                "Dominican Republic", "East Timor", "Ecuador", "Egypt", "El Salvador",
                "England", "Equatorial Guinea", "Eritrea", "Estonia", "Ethiopia",
                "Falkland Islands", "Faroe Islands", "Fiji", "Finland", "France",
                "Gabon", "Gambia", "Georgia", "Germany", "Ghana",
                "Gibraltar", "Great Britain", "Greece", "Greenland", "Grenada",
                "Guadeloupe", "Guam", "Guatemela", "Guernsey", "Guiana",
                "Guinea", "Guinea Bissau", "Guyana", "Haiti", "Heard Islands",
                "Honduras", "Hong Kong", "Hungary", "Iceland", "India",
                "Indonesia", "Iran", "Iraq", "Ireland", "Isle Of Man",
                "Israel", "Italy", "Jamaica", "Japan", "Jersey",
                "Jordan", "Kazakhstan", "Kenya", "Kiribati", "Korea, South",
                "Korea, North", "Kuwait", "Kyrgyzstan", "Lao People's Dem. Rep.", "Latvia",
                "Lebanon", "Lesotho", "Liberia", "Libya", "Liechtenstein",
                "Lithuania", "Luxembourg", "Macau", "Macedonia", "Madagascar",
                "Malawi", "Malaysia", "Maldives", "Mali", "Malta",
                "Mariana Islands", "Marshall Islands", "Martinique", "Mauritania", "Mauritius",
                "Mayotte", "Mexico", "Micronesia", "Moldova", "Monaco",
                "Mongolia", "Montserrat", "Morocco", "Mozambique", "Myanmar",
                "Namibia", "Nauru", "Nepal", "Netherlands", "Netherlands Antilles",
                "Neutral Zone", "New Caledonia", "New Zealand", "Nicaragua", "Niger",
                "Nigeria", "Niue", "Norfolk Island", "Northern Ireland", "Norway",
                "Oman", "Pakistan", "Palau", "Panama", "Papua New Guinea",
                "Paraguay", "Peru", "Philippines", "Pitcairn", "Poland",
                "Polynesia", "Portugal", "Puerto Rico", "Qatar", "Reunion",
                "Romania", "Russian Federation", "Rwanda", "Saint Helena", "Saint Kitts",
                "Saint Lucia", "Saint Pierre", "Saint Vincent", "Samoa", "San Marino",
                "Sao Tome and Principe", "Saudi Arabia", "Scotland", "Senegal", "Seychelles",
                "Sierra Leone", "Singapore", "Slovakia", "Slovenia", "Solomon Islands",
                "Somalia", "South Africa", "South Georgia", "Spain", "Sri Lanka",
                "Sudan", "Suriname", "Svalbard", "Swaziland", "Sweden",
                "Switzerland", "Syrian Arab Republic", "Taiwan", "Tajikista", "Tanzania",
                "Thailand", "Togo", "Tokelau", "Tonga", "Trinidad and Tobago",
                "Tunisia", "Turkey", "Turkmenistan", "Turks and Caicos Islands", "Tuvalu",
                "Uganda", "Ukraine", "United Arab Emirates", "United Kingdom", "United States",
                "Uruguay", "Uzbekistan", "Vanuatu", "Vatican City State", "Venezuela",
                "Vietnam", "Virgin Islands", "Wales", "Western Sahara", "Yemen",
                "Yugoslavia", "Zaire", "Zambia", "Zimbabwe"
            };
    }
}

}

有什么建议吗？感谢