gistfile1.cs

var foo = new Foo();
var bar = typeof(Foo).GetMethod("Bar");

var param = Expression.Parameter(typeof(int));
var bar2 = Expression.Lambda<Func<int, string>>(
    Expression.Call(Expression.Constant(foo), bar, param), param).Compile();

var s = Stopwatch.StartNew();
for (int i = 0; i < 5000000; i++)
    foo.Bar(i);

Console.WriteLine("Sem reflection: {0}", s.Elapsed);

s.Restart();
for (int i = 0; i < 5000000; i++)
    bar2.Invoke(i);

Console.WriteLine("Com reflection: {0}", s.Elapsed);