Shimano had a component line right under the top of the line Deore XT line called the Deore DX group. It was almost as nice looking as the XT group and probably worked just as good as the high end group but it was still a relatively popular group.
The Deore DX group evolved from the Deore group that had been with Shimano since 1984 and was quickly establised as a dependable MTB group for enthusiasts and racers on budget.
The rear derailleur is a solid unit working great under all kind of action in the woods. Available in either long or short cage, this long cage derailleur is ready to hit the dirt anytime. Maybe a bit more hardcore than XT, this is the real deal that can take punishment and wont break your bank if you break it.
You can give it a shot at breaking it for 20 Euro.