It will work to some extent. But you cannot the performance what you are gaining with the workstation card!
If you are doing parts & some simple assemblies with around 20-30 parts mean ,5850 will be ok! if you are going to use much big assemblies with more components or Complicated profile components meants 5850 won't help you!
You can go with beginner card like Quadro 580http://www.newegg.com/Product/Product.aspx?Item=N82E16814133273
It'll work better than 5850 for UG NX6!