It really depends on what you want to do with it and how much you believe in "terms". The field model is somewhat lighter than the sporting model and usually will have looks that are not up to par with the sporting model, but not necessarily so.
You can shoot sporting clays with the field model as well as you can the sporting model. The sporting is an upgrade, usually in wood and decoration.
There will be some differences other than these. Is the sporting worth the extra money? You'll have to decide that one for yourself!
Good Shooting,
