I have a collie and a kelpie. Two bitches, 3 and 4 years old. Cracking little dogs, high pray drive and great at ratting and driving out rabbits. Looking at getting a running dog to join the pack but no idea what to go for. I have seen a few patterdale x whippets work and beddyx whippets but not sure if a bigger dog would be better suited. Any advice/ recommendations would be great. Thank you