This test shows you that Linq to object is significantly slower than traditional for loop.

LinqSlowerThanLoop.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Reflection;
using System.Linq.Expressions;
using System.Reflection.Emit;
using System.IO;
using System.Diagnostics;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] list = new int[] { 1, 2, 3, 4, 5 };
            Stopwatch sw = new Stopwatch();

            int n = 10000000;
            sw.Start();
            for (int i = 0; i < n; i++)
            {
                list.Select(x => 2 * x).ToArray();
            }
            sw.Stop();
            Console.WriteLine("select: " + sw.ElapsedMilliseconds);

            sw.Reset();
            sw.Start();
            for (int i = 0; i < n; i++)
            {
                int size = list.Length;
                int[] newList = new int[size];
                for (int j = 0; j < size; j++)
                {
                    newList[j] = list[j] * 2;
                }
            }
            sw.Stop();
            Console.WriteLine("loop: " + sw.ElapsedMilliseconds);
            
            // linq: 3043
            // loop: 242
        }
    }
}