I'm not sure about those specific guns, so I can't comment on the price difference specifically, but I will say that if you're just starting and going at it for fun (and not to be a top level competitor) a field gun is fine. But if you want a dedicated sporting gun, that's great too.
I have found that a lot of "sporting" guns have better wood on them, as well as a stock design that would lend itself more towards customization, so that could be one source of the price difference you're noticing.
Also for a competition gun, I'd replace all of the chokes anyway. I haven't found a single OEM choke that patterns well. It doesn't mean there isn't one out there, but everyone I know uses aftermarket chokes (usually Briley). Extended chokes just make them easier to get out and let you rest the barrel on your toe without worrying about scuffing the barrel itself. The difference in pattern between extended and regular chokes is negligible in my experience. Especially if you extend the forcing cone.
Also, the "sporting" gun *may* have lighter or better triggers (one physical trigger, but 2 mechanisms, one for each barrel). I would take that with a grain of salt though, as my Citori had horrible triggers out of the box. One was pushing 4 lbs and the other was over 5.5 lbs. I got them taken down to 3.25 lbs each.