The stumpiness should be avoided in the way that I base them. I'm planning to have them leaping over rocky outcrops so they will have a great deal of height to them, some may even appear to be standing on their hind legs.
From what you've all said I think I will settle for the Fenrisian Wolves. I much prefer the look and now I've seen a good comparison with the Fell Wargs they just look so much more feral and aggressive, and perfect for carrying the bulk of Uruk Hai scouts upon their backs.
Thanks everyone, your help has been greatly appreciated, and inspired my first evil army attempt in over 8 years since I spray painted a Balrog black and dry brushed it with Golden Yellow - simply awful!! Hopefully this project will turn out much better!