From what you have said about the large warren, i think a 50 yrd longnet would be the best option.
But obviously, you are wanting to go a step further with the running dogs as well!
A pure whippet will do the job, and do it well. If you need a little more durability then think about a cross, maybee collie type, but don't be afraid to just get a bigger collie/ grey, they will not take up much more space! a dog is a dog, big or small!