Ускорить сравнение двух List<> - C#

    class Item : IEquatable<Item>, IComparable<Item>
    {
        public string Link  { get; private set; }
        public string Name  { get; private set; }
        public string Owner { get; private set; }
 
        public Item(string link, string owner)
        {
            Owner = owner;
            Link = link;
            string[] tmp = link.Split('/');
            Name = tmp[tmp.Length - 1];
        }
        public bool Equals(Item other)
        {
            return other != null && other.Link == this.Link;
        }
        public int CompareTo(Item other)
        {
            return string.Compare(this.Link, other.Link);
        }
    }

    class Program
    {
        static List<Item> allItems = new List<Item>();
        static List<Item> oldItems = new List<Item>();
        ...
        static List<Item> GetNewItems()
        {
            List<Item> newItems = new List<Item>();
            foreach (var item in allItems)
            {
                if (!oldItems.Contains(item))
                    newItems.Add(item);
            }
            return newItems;
        }